Link Budget Calculator
Calculate RF link margin, received power, EIRP, free-space path loss, maximum free-space range, MAPL, and Fresnel-zone clearance.
Calculator is for informational and preliminary engineering purposes only. Terms and Conditions
Uses free-space path loss for an unobstructed line-of-sight path; terrain, diffraction, multipath, atmospheric absorption, rain, foliage, and interference are not automatically modeled.
Enter the link values
Use the radio, antenna, feedline, path, and receiver values for the direction you want to analyze.
Receiver sensitivity must match the intended modulation and data rate. Gains are positive; cable, connector, and other losses are entered as positive loss values.
Link result
Link margin is shown first, followed by received power and design checks.
Link details
- Received power—
Show calculation steps Review conversions, FSPL, EIRP, received power, link margin, MAPL, range, and Fresnel clearance
- Enter valid values to see the complete calculation.
RF link budget breakdown
Relative magnitudes of the gain and loss terms applied between transmitter output and receiver input.
- Enter valid values to populate the link budget.
Method, Sources, and Assumptions
Calculation basis, current ITU-R references, model limitations, and final verification requirements.
Free-space attenuation is calculated from the current ITU-R P.525 relationship. First-Fresnel-zone radius is provided as a geometry check; the 60% clearance value is a common wireless planning guideline, not a universal ITU requirement. The calculator does not calculate terrain diffraction or a complete propagation reliability model.
- Free-space path loss assumes an unobstructed propagation path and does not by itself predict real-world availability or fading.
- Other fixed losses are subtracted as entered; use measured or defensible project-specific values and avoid double-counting.
- The required design margin is a user input, not a universal standard or guaranteed reliability threshold.
- Verify terrain, diffraction, Earth curvature, antenna patterns and alignment, polarization, atmospheric and rain effects, interference, regulatory EIRP limits, and manufacturer data for real designs.
Calculator guide
How to Read a Link Budget
A link budget tracks RF power from the transmitter to the receiver and compares the estimated receiver-input power with receiver sensitivity. The RF Link Budget Calculator above uses transmit power, antenna gains, cable losses, frequency, distance, receiver sensitivity, and optional additional losses to calculate link margin, received power, EIRP, free-space path loss, maximum allowable path loss, theoretical free-space range, wavelength, and first-Fresnel-zone clearance.
The practical question is not only whether link margin is positive. A real wireless link also needs enough reserve for the intended reliability target and an adequately clear propagation path. The calculator therefore separates available link margin from the required design margin you enter.
- Primary output
- Link margin in dB
- Best for
- Preliminary point-to-point RF and wireless link checks
- Key assumption
- Free-space propagation unless known extra losses are entered
How to Use the Link Budget Calculator
Use values for one direction of the radio link at a time. The wireless link budget calculator updates automatically, so the main task is entering each gain and loss at the correct point in the RF chain and using receiver sensitivity for the actual operating mode you want to support.
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Enter transmitter power before the TX feedline
Use the conducted transmitter output, not EIRP. The calculator accepts dBm, dBW, watts, or milliwatts and converts them to the same internal power basis.
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Enter TX antenna gain and transmitter-side losses
Use antenna gain toward the receiving site in dBi or dBd. Enter cable and connector attenuation as a positive loss value; the calculator subtracts that loss when calculating EIRP.
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Enter operating frequency and path distance
Frequency may be entered in Hz, kHz, MHz, or GHz, and distance in meters, kilometers, feet, or miles. These values determine the free-space path loss and wavelength used by the calculator.
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Enter receiver-side gain, loss, and sensitivity
Use RX antenna gain toward the transmitting site, the feedline or connector loss between the RX antenna and receiver, and the receiver sensitivity for the modulation, coding, bandwidth, data rate, and performance criterion that matter to the link.
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Add only known additional losses
The Other fixed losses field can represent known polarization mismatch, pointing loss, penetration loss, foliage loss, or another defensible penalty that is not already included elsewhere. Avoid counting the same loss twice.
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Set the required design margin
The required margin is a user-selected reserve above receiver sensitivity. It should come from the reliability objective, propagation analysis, project specification, or another defensible design basis rather than from a universal rule.
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Read link margin first, then check the supporting results
A positive link margin means calculated receiver-input power is above the entered sensitivity. Compare that value with your design-margin target, then review EIRP, FSPL, MAPL, theoretical maximum distance, and Fresnel clearance before relying on the result for a real installation.
Where to Get the Link Budget Inputs
The arithmetic is straightforward, but the quality of the result depends on using values from the correct physical reference point. When possible, use measured installation data or manufacturer specifications for the actual operating frequency and radio mode.
| Input | Best source or check |
|---|---|
| Transmit power | Radio configuration or manufacturer data for conducted output power at the intended operating mode. |
| TX antenna gain | Manufacturer radiation-pattern data or a verified gain calculation in the direction of the receiving site. |
| TX cable / connector loss | Measured assembly loss or cable and connector data adjusted for the installed length and operating frequency. |
| Frequency | Actual carrier or center frequency for the channel being evaluated. |
| Distance | Straight-line endpoint geometry from surveyed coordinates, GIS/path data, or another reliable site measurement. |
| RX antenna gain | Manufacturer pattern data or a verified gain calculation toward the transmitting site. |
| RX cable / connector loss | Measured or frequency-adjusted passive loss between the receive antenna and receiver input. |
| Receiver sensitivity | Manufacturer data for the exact bandwidth, modulation, coding, data rate, and performance criterion you need. |
| Other fixed losses | Measured loss or a defensible project-specific propagation or installation allowance that is not already counted elsewhere. |
| Required design margin | Project reliability objective, propagation study, specification, or other documented engineering criterion. |
A particularly important input is receiver sensitivity. For example, if a hypothetical radio were rated at −98 dBm in one low-rate mode and −82 dBm in a higher-rate mode, using the wrong value would shift the calculated margin by 16 dB even though the physical path had not changed.
Link Budget Formula and Method
The calculator is a multi-step RF power budget. It first calculates transmitter EIRP, subtracts free-space propagation loss and other losses, adds receive antenna gain, and then compares receiver-input power with receiver sensitivity.
Received-power equation
Plain language: start with transmitter power, add the antenna gains, and subtract transmitter losses, free-space path loss, receiver losses, and any additional fixed losses.
Equivalent isotropically radiated power
EIRP combines conducted transmitter power, TX antenna gain, and TX feedline loss into one radiated-power reference.
Free-space path loss
Distance is in meters, frequency is in hertz, and \(c\) is the speed of light. This is the free-space attenuation relationship represented in current ITU-R P.525-5.
Common km and MHz FSPL form
This is a convenient manual-check form when distance is in kilometers and frequency is in megahertz. The production calculator instead evaluates the relationship directly using the speed of light.
Link margin and design reserve
Link margin is received power minus receiver sensitivity. The calculator also reports remaining design reserve as \(M-M_{target}\), where \(M_{target}\) is the required design margin entered by the user.
Maximum allowable path loss
MAPL is the largest propagation loss that still leaves the required design margin above receiver sensitivity.
Maximum free-space distance
This reverses the free-space path-loss equation. The result is a theoretical free-space distance, not a terrain-aware coverage radius.
- \(P_R\)
- Received power Estimated power at the receiver input after the entered gains and losses.
- \(P_T\)
- Transmit power Conducted transmitter output before transmitter-side feedline loss.
- \(G_T\)
- TX antenna gain Transmit-antenna gain in the direction of the receiving site.
- \(L_T\)
- TX cable and connector loss Passive attenuation between transmitter output and TX antenna.
- \(L_{FS}\)
- Free-space path loss Ideal propagation attenuation caused by geometric spreading over the entered distance and frequency.
- \(G_R\)
- RX antenna gain Receive-antenna gain toward the transmitting site.
- \(L_R\)
- RX cable and connector loss Passive attenuation between the RX antenna and receiver input.
- \(L_{other}\)
- Other fixed losses Additional known attenuation not already represented by the dedicated cable, antenna, or free-space terms.
- \(P_{sens}\)
- Receiver sensitivity Minimum receiver-input power for the selected operating mode or performance criterion.
- \(M\)
- Link margin Difference between estimated received power and receiver sensitivity.
- \(M_{target}\)
- Required design margin User-selected reserve required above receiver sensitivity.
- \(d\)
- Path distance Straight-line propagation distance used by the free-space model.
- \(f\)
- Frequency Carrier or center frequency used to calculate free-space path loss and wavelength.
- \(c\)
- Speed of light The calculator uses 299,792,458 meters per second for wavelength and free-space path-loss calculations.
Fast dB sanity checks
With every other entered term held constant, adding 1 dB of transmit power or antenna gain adds 1 dB to received power and link margin. Adding 1 dB of loss removes 1 dB. Doubling free-space distance increases FSPL by \(20\log_{10}(2)\approx6.02\) dB, while halving distance reduces it by the same amount.
Doubling frequency also adds approximately 6.02 dB of FSPL when distance and the numerical antenna gains are held constant. That does not mean a higher-frequency system always has less range, because the achievable gain of a fixed physical antenna aperture can also vary with frequency.
Worked Link Budget Example
Use the same illustrative state loaded by the calculator: a 2.4 GHz, 2 km link with 20 dBm transmitter output, 6 dBi antennas at both ends, 1 dB of cable and connector loss at each end, −90 dBm receiver sensitivity, no extra fixed loss, and a 10 dB required design margin.
Calculate EIRP
Calculate free-space path loss
Calculate received power
Calculate link margin
Compare with the required margin
Result
Link margin ≈ +13.93 dB
The free-space model places receiver-input power about 13.93 dB above the entered receiver sensitivity. With a 10 dB required design margin, the example retains approximately 3.93 dB of remaining design reserve, so it passes the entered target under the calculator’s assumptions.
How to Interpret the Results
Treat link margin as the primary closure check, then use received power, design reserve, MAPL, theoretical range, wavelength, and Fresnel clearance to understand the result and decide what needs to be verified next.
Link margin tells you how far the estimate is above sensitivity
If link margin is negative, calculated receiver-input power is below the entered sensitivity. If it is positive, the basic modeled budget closes. A positive value alone does not establish real-world availability, throughput, or error performance.
Design reserve tells you whether your own target is met
The calculator subtracts required design margin from available link margin. A positive reserve means the modeled link exceeds the selected design target; a negative reserve means the link may close while still falling short of that target.
Received power is the estimated receiver-input level
This is the power remaining after the modeled transmit chain, propagation loss, receive antenna gain, and receiver-side losses have been applied. It should be compared with sensitivity for the same receiver operating mode.
EIRP is not the same as radio output power
EIRP includes TX antenna gain and TX-side loss. If the radio produces 20 dBm but antenna gain and cable loss change, EIRP changes even though conducted transmitter output remains 20 dBm.
MAPL is a loss limit, not a distance
Maximum allowable path loss is the propagation loss the budget can tolerate while preserving the chosen margin. Converting MAPL to range requires a propagation model; this calculator uses free-space attenuation.
The maximum distance result is an idealized free-space value
It answers how far the same mathematical budget could extend if free-space attenuation were the governing path-loss mechanism. It does not include terrain, clutter, diffraction, fading, weather, or interference.
Fresnel clearance is a path-geometry check
The calculator reports the first Fresnel-zone radius at the path midpoint and 60% of that radius. Current ITU-R P.526-16 covers Fresnel zones and diffraction concepts, but the calculator does not know obstacle or terrain heights, so the value does not prove that the path is clear.
Link margin vs fade margin
In this calculator, link margin is defined as received power minus receiver sensitivity. Required design margin is the reserve you want the system to maintain above sensitivity. The term fade margin is used differently across organizations: some use it approximately as a synonym for available link margin, while others reserve it for the portion of margin allocated specifically to fading. Always check the convention used by the specification, spreadsheet, or propagation method you are comparing against.
How common changes affect link margin
| Change | Approximate effect on link margin |
|---|---|
| +1 dB TX power | +1 dB |
| +1 dB TX antenna gain | +1 dB |
| +1 dB RX antenna gain | +1 dB |
| +1 dB TX cable loss | −1 dB |
| +1 dB RX cable loss | −1 dB |
| +1 dB other fixed loss | −1 dB |
| Double free-space distance | About −6.02 dB |
| Half free-space distance | About +6.02 dB |
| Double frequency with antenna gains held fixed | About −6.02 dB |
Check both directions for a two-way link
For endpoint A to endpoint B, use A’s transmit power and TX losses with B’s RX antenna gain, RX losses, and receiver sensitivity. Then repeat the calculation from B to A using the opposite equipment values. If two-way communication is required, the weaker direction can govern usable performance.
Real-World RF Losses the Free-Space Model Does Not Predict
Free-space path loss is a baseline rather than a complete field-propagation model. Real installations can depart from that baseline because RF energy can be blocked, diffracted, reflected, absorbed, misdirected, or limited by interference and noise.
Terrain and obstruction diffraction
Hills, buildings, ridges, and other obstructions can add diffraction loss that is not part of FSPL. Use an elevation and obstacle profile with an appropriate diffraction method when the path is not demonstrably clear. ITU-R P.526-16 is the current ITU-R diffraction recommendation.
Fresnel-zone obstruction
An optical line of sight can exist while part of the Fresnel zone is obstructed. The first Fresnel-zone radius at a point along the path is
At the midpoint of a symmetric path, this simplifies to \(r_1=\sqrt{\lambda d/4}\), which is the midpoint relationship used by the calculator.
Multipath and atmospheric refractivity
Reflections and changing refractivity can produce fading even when geometric line of sight exists. ITU-R P.530-19 provides terrestrial line-of-sight propagation and outage methods for design work where availability matters.
Atmospheric gases
Oxygen and water vapor can introduce frequency- and path-dependent attenuation. Current ITU-R P.676-13 covers attenuation by atmospheric gases and related effects. Use a path-specific model where this loss is material rather than assigning an arbitrary generic penalty.
Rain and hydrometeors
Rain attenuation can become important for some microwave and millimeter-wave paths and varies with frequency, polarization, precipitation statistics, geometry, and availability target. Serious terrestrial LOS designs should use an appropriate rain and reliability method rather than treating FSPL as total propagation loss.
Foliage and building penetration
Trees, walls, roofs, vehicles, and other material in the propagation path can add loss that free space cannot predict. Use measured data or a propagation method that represents the actual environment and frequency.
Antenna pattern and pointing
The gain entered into a link budget should apply in the actual path direction. Peak catalog gain can overstate installed link gain when the antenna is off-axis, tilted incorrectly, partially obstructed, or operating outside the conditions represented by the specification.
Polarization mismatch
Transmit and receive polarization need to be compatible. A polarization mismatch can reduce received signal level without changing free-space loss, so known mismatch loss belongs in the system budget rather than in the FSPL term.
Interference and receiver noise
A receiver can have enough wanted-signal power and still perform poorly if interference or noise prevents the required signal-to-noise or signal-to-interference ratio. A pure link budget does not replace an interference analysis.
Receiver sensitivity depends on operating mode
The same receiver may have different sensitivity values for different bandwidths, modulations, coding rates, and data rates. Use the manufacturer value associated with the mode you actually need to support.
Common Link Budget Mistakes
Large link-budget errors usually come from using the wrong reference point, mixing logarithmic units, double-counting a loss, using the wrong receiver sensitivity, or assuming free-space loss represents the complete path.
Entering EIRP as transmitter power
The TX power field expects conducted transmitter output. If EIRP is entered there and TX antenna gain is also entered, antenna gain is counted twice. Enter the radio output first and let the calculator calculate EIRP.
Confusing dBm, dB, dBi, and dBd
dBm and dBW represent absolute power levels. dB represents a logarithmic ratio or gain/loss, while dBi and dBd are antenna-gain references. They can appear in the same budget but do not represent the same physical quantity.
Entering losses as negative values
The loss fields are already subtracted by the calculator. A 2 dB cable loss should therefore be entered as 2 dB, not −2 dB. Entering a negative loss would mathematically behave like gain.
Double-counting a loss
If a measured cable loss is entered in the dedicated TX or RX loss field, do not include that same loss again in Other fixed losses. Keep a clear inventory of which losses are already represented in antenna specifications, equipment data, or measurements.
Using peak antenna gain in the wrong direction
An antenna’s maximum dBi value applies to its peak-gain direction. If the other endpoint lies away from that direction, the applicable gain can be lower than the headline specification.
Using the wrong receiver sensitivity
Receiver sensitivity is not one universal value for every radio mode. Use the manufacturer’s sensitivity for the bandwidth, modulation, coding, data rate, and performance criterion that correspond to the planned link.
Assuming visible line of sight equals free space
Seeing the far antenna does not prove that the Fresnel zone is adequately clear, and it does not eliminate multipath, weather, atmospheric, or interference effects. Optical line of sight is only one part of path verification.
Treating positive margin as guaranteed reliability
A +1 dB link margin means the modeled received signal is only 1 dB above the entered sensitivity. Reliability targets need a separately justified design margin and, when consequences warrant it, a propagation and availability analysis appropriate to the link.
Checking only one direction
Bidirectional systems can be asymmetric. Repeat the calculation with the endpoints reversed when transmit power, sensitivity, frequency, antenna gain, or feedline loss differs by direction. The weaker direction may govern the usable connection.
Assumptions and Limits
This link budget calculator is a preliminary RF planning tool. The power-accounting arithmetic is transparent, but the propagation portion is intentionally limited to free-space attenuation plus any additional fixed loss that you explicitly enter.
Free-space propagation is the baseline
The calculator does not derive terrain, diffraction, clutter, multipath, atmospheric-gas, rain, foliage, or interference loss from site conditions. Those effects require additional data and an appropriate propagation model when they matter.
Maximum range is theoretical
The maximum-distance outputs are obtained by applying the free-space relationship to MAPL. They are not service radii, coverage guarantees, regulatory contours, or substitutes for terrain-aware path studies.
Fresnel results do not verify obstacle clearance
The calculator returns midpoint first-Fresnel-zone radius and a 60% clearance value from frequency and total distance. It does not know antenna elevations, obstacle heights, terrain, Earth curvature, or atmospheric refraction.
Required design margin is not universal
The calculator treats required margin as a user input because the amount of reserve needed depends on the reliability target and unmodeled propagation, installation, interference, and equipment factors.
Receiver sensitivity must match the intended mode
The result assumes the entered sensitivity applies to the operating bandwidth, modulation, coding, data rate, and performance criterion that you require. Changing operating mode can change margin even if every propagation input remains the same.
Calculated EIRP does not establish regulatory compliance
The tool calculates an RF EIRP quantity but does not determine whether that value is permitted for a particular frequency band, radio service, jurisdiction, device certification, antenna configuration, or license.
A satellite link can require additional system terms
A preliminary free-space received-power budget can be useful for a satellite path, but complete satellite communications analysis may also require quantities such as noise temperature, \(C/N_0\), \(E_b/N_0\), polarization loss, pointing loss, atmospheric attenuation, and separate uplink and downlink performance.
Engineering Sources
The free-space method and propagation-limit discussion were checked against current ITU-R recommendations. The worked example was independently recomputed from the exact free-space equation and checked by solving the MAPL relationship backward for distance.
- ITU-R P.525-5 — Calculation of free-space attenuation — Current 11/2024 in-force recommendation supporting the free-space attenuation relationship used by the calculator.
- ITU-R P.526-16 — Propagation by diffraction — Current 11/2025 in-force recommendation covering Fresnel-zone and diffraction concepts used to explain path-clearance limits.
- ITU-R P.530-19 — Propagation data and prediction methods required for the design of terrestrial line-of-sight systems — Current 09/2025 in-force recommendation for terrestrial LOS propagation and reliability analysis beyond a basic free-space budget.
- ITU-R P.676-13 — Attenuation by atmospheric gases and related effects — Current in-force recommendation covering atmospheric-gas attenuation where that effect is material to the path.
The calculator uses 299,792,458 m/s for the speed of light and calculates free-space loss directly from distance and frequency. Display rounding does not change the underlying calculation.
Link Budget FAQ
These questions address common interpretation and application issues that are not fully answered by the calculation alone.
What is a good link margin?
There is no universal link-margin value that guarantees every RF link will be reliable. The required reserve depends on the frequency, path, environment, desired availability, interference, weather, equipment behavior, modulation, and other losses. Use a margin supported by the reliability objective and propagation analysis for the specific system.
What is the difference between link margin and fade margin?
In this calculator, link margin is received power minus receiver sensitivity, while required design margin is the user-selected reserve above sensitivity. “Fade margin” is not used identically in every organization, so check the definition used by the specification or propagation method you are comparing against.
Does line of sight guarantee a wireless link will work?
No. Optical line of sight does not prove adequate Fresnel-zone clearance and does not remove multipath, atmospheric effects, rain, interference, antenna misalignment, or equipment limitations. It is one path condition rather than a complete reliability test.
Can the calculator estimate maximum RF range?
Yes. It reverses the free-space path-loss relationship using the calculated maximum allowable path loss. The resulting distance is a theoretical free-space value and should not be interpreted as guaranteed real-world coverage.
Can this calculator be used for Wi-Fi or LoRa?
Yes, for a preliminary free-space RF power budget when the required transmitter, antenna, path, and sensitivity inputs are known. Use receiver sensitivity for the exact Wi-Fi rate or LoRa operating mode being evaluated, and account separately for the actual indoor, outdoor, foliage, terrain, interference, and installation environment.
Can this calculator be used for microwave links?
It is useful as a first-pass power budget, but consequential terrestrial microwave design can require terrain and diffraction analysis, Fresnel clearance, atmospheric attenuation, rain fading, multipath analysis, antenna alignment, and availability calculations in addition to the free-space link budget.
Can this calculator be used for satellite links?
It can provide a preliminary free-space received-power budget, but a complete satellite link analysis may require separate uplink and downlink budgets plus noise temperature, \(G/T\), \(C/N_0\), \(E_b/N_0\), atmospheric attenuation, rain, polarization, pointing, and transponder or receiver-specific terms that are outside this calculator.