Interactive selector
Calculate Voltage Drop for Every Wire Size
The table recalculates standard AWG and kcmil rows and marks the smallest listed conductor at or below your target.
Current scenario: 120 V, 15 A, 50 ft one-way, copper, single-phase AC, 3.00% maximum drop.
“First qualifying” refers only to the selected voltage-drop target. It is not an ampacity, protection, termination, or code-compliance approval.
Calculated comparison
Voltage Drop Results by Standard Wire Size
Compare AWG and kcmil sizes, including circular-mil and approximate metric area, then select up to five rows for the chart.
Rows are ordered by conductor area. The highlighted row is the smallest listed size that meets the active target using the displayed preliminary method.
No conductor rows match the current search or status filter.
| Compare | Target status | Copy | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 18 AWG | 1,620 / 0.82 | 11.944 V | 9.95% | 108.06 V | Fails 3.00% | 179.2 W | 15.1 ft | ||
| 16 AWG | 2,580 / 1.31 | 7.500 V | 6.25% | 112.50 V | Fails 3.00% | 112.5 W | 24.0 ft | ||
| 14 AWG | 4,110 / 2.08 | 4.708 V | 3.92% | 115.29 V | Fails 3% | 70.6 W | 38.2 ft | ||
| 12 AWG | 6,530 / 3.31 | 2.963 V | 2.47% | 117.04 V | First qualifying | 44.4 W | 60.7 ft | ||
| 10 AWG | 10,380 / 5.26 | 1.864 V | 1.55% | 118.14 V | Passes 3% | 28.0 W | 96.6 ft | ||
| 8 AWG | 16,510 / 8.37 | 1.172 V | 0.98% | 118.83 V | Passes 3% | 17.6 W | 153.6 ft | ||
| 6 AWG | 26,240 / 13.30 | 0.737 V | 0.61% | 119.26 V | Passes 3% | 11.1 W | 244.1 ft | ||
| 4 AWG | 41,740 / 21.15 | 0.464 V | 0.39% | 119.54 V | Passes 3% | 7.0 W | 388.3 ft | ||
| 3 AWG | 52,620 / 26.66 | 0.368 V | 0.31% | 119.63 V | Passes 3% | 5.5 W | 489.5 ft | ||
| 2 AWG | 66,360 / 33.63 | 0.292 V | 0.24% | 119.71 V | Passes 3% | 4.4 W | 617.3 ft | ||
| 1 AWG | 83,690 / 42.41 | 0.231 V | 0.19% | 119.77 V | Passes 3% | 3.5 W | 778.5 ft | ||
| 1/0 AWG | 105,600 / 53.51 | 0.183 V | 0.15% | 119.82 V | Passes 3% | 2.7 W | 982.3 ft | ||
| 2/0 AWG | 133,100 / 67.44 | 0.145 V | 0.12% | 119.85 V | Passes 3% | 2.2 W | 1238.1 ft | ||
| 3/0 AWG | 167,800 / 85.03 | 0.115 V | 0.10% | 119.88 V | Passes 3% | 1.7 W | 1560.9 ft | ||
| 4/0 AWG | 211,600 / 107.22 | 0.091 V | 0.08% | 119.91 V | Passes 3% | 1.4 W | 1968.4 ft | ||
| 250 kcmil | 250,000 / 126.68 | 0.077 V | 0.06% | 119.92 V | Passes 3% | 1.2 W | 2325.6 ft | ||
| 300 kcmil | 300,000 / 152.01 | 0.065 V | 0.05% | 119.94 V | Passes 3% | 1.0 W | 2790.7 ft | ||
| 350 kcmil | 350,000 / 177.35 | 0.055 V | 0.05% | 119.94 V | Passes 3% | 0.8 W | 3255.8 ft | ||
| 400 kcmil | 400,000 / 202.68 | 0.048 V | 0.04% | 119.95 V | Passes 3% | 0.7 W | 3720.9 ft | ||
| 500 kcmil | 500,000 / 253.35 | 0.039 V | 0.03% | 119.96 V | Passes 3% | 0.6 W | 4651.2 ft | ||
| 600 kcmil | 600,000 / 304.02 | 0.032 V | 0.03% | 119.97 V | Passes 3% | 0.5 W | 5581.4 ft | ||
| 750 kcmil | 750,000 / 380.03 | 0.026 V | 0.02% | 119.97 V | Passes 3% | 0.4 W | 6976.7 ft | ||
| 1000 kcmil | 1,000,000 / 506.71 | 0.019 V | 0.02% | 119.98 V | Passes 3% | 0.3 W | 9302.3 ft |
Calculated values use a simplified circular-mil K-factor estimate. Real conductor resistance varies with temperature, construction, installation, AC effects, and source data.
Table and export options
Selected-row chart
Compare Voltage Drop by Conductor Size
The chart automatically follows the decision boundary: the last failing row, the first qualifying row, and nearby passing rows.
Select conductor rows in the table to compare voltage-drop percentage.
How to Interpret the Highlighted Row
The highlighted row answers a narrow question: which listed conductor first meets the chosen voltage-drop percentage under the entered assumptions. It does not determine the final conductor by itself.
Voltage Drop Is Not an Ampacity Check
Design limitation
Confirm conductor ampacity, overcurrent protection, insulation rating, terminal temperature limits, ambient correction, conductor bundling, raceway fill, grounding, fault duty, equipment instructions, and the locally adopted electrical code. A row can pass voltage drop and still be unacceptable for installation.
Voltage Drop Equations Used by This Table
For a two-wire DC or single-phase circuit, the preliminary circular-mil relationship is:
The entered length is one-way. The factor of 2 represents the outgoing and return conductor path.
For a balanced three-phase circuit:
The result is an approximate line-to-line voltage drop for balanced loading.
Variables
- Vdvoltage drop, volts
- Kmaterial resistivity constant in ohm-cmil/ft
- Iload current, amperes
- Lone-way length, feet
- CMconductor area, circular mils
Percentage drop is calculated as 100 × Vd ÷ source voltage. The solver keeps full internal precision and rounds only the displayed values.
3% and 5% Voltage Drop Guidance
Three percent is a common design target for an individual branch circuit, while five percent is often used as a combined feeder-plus-branch design target. These values should not be treated as one universal legal limit for every circuit or piece of equipment.
| Source voltage | 1% | 2% | 3% | 5% |
|---|---|---|---|---|
| 12 V | 0.12 V | 0.24 V | 0.36 V | 0.60 V |
| 24 V | 0.24 V | 0.48 V | 0.72 V | 1.20 V |
| 48 V | 0.48 V | 0.96 V | 1.44 V | 2.40 V |
| 120 V | 1.20 V | 2.40 V | 3.60 V | 6.00 V |
| 208 V | 2.08 V | 4.16 V | 6.24 V | 10.40 V |
| 240 V | 2.40 V | 4.80 V | 7.20 V | 12.00 V |
| 277 V | 2.77 V | 5.54 V | 8.31 V | 13.85 V |
| 480 V | 4.80 V | 9.60 V | 14.40 V | 24.00 V |
Worked Example: 120 V, 15 A, 50 ft Copper Circuit
12 AWG calculation
Assumptions: copper, single-phase/two-wire, 50 ft one-way, 6,530 cmil.
Vd = 2 × 12.9 × 15 × 50 ÷ 6,530 ≈ 2.96 V.
Percentage drop ≈ 2.96 ÷ 120 × 100 = 2.47%.
Interpretation
At a 3% target, 14 AWG exceeds the target while 12 AWG is the first listed size below it in this simplified comparison.
The next step is to verify ampacity and every installation requirement independently.
Common Voltage Drop Calculation Mistakes
Entering round-trip length
This tool expects one-way source-to-load distance and applies the circuit multiplier internally.
Using breaker rating automatically
Use the design or operating current appropriate to the engineering check. Breaker rating and actual load current are not always interchangeable.
Ignoring feeder drop
A branch-circuit target does not erase voltage drop already consumed upstream in a feeder.
Rounding too early
Pass or fail is evaluated from the unrounded result, even when the displayed percentage appears equal to the target.
Assuming copper and aluminum are interchangeable
Different material constants change the calculated drop and may change the first qualifying size.
Treating the result as approval
The table is a preliminary design aid, not a substitute for project-specific engineering or code review.
Engineering Basis and Source Transparency
Original calculated output; no complete NEC or IEEE conductor-impedance table is reproduced.
The interactive table uses a simplified circular-mil K-factor method for preliminary comparison. It is intentionally separated from detailed impedance calculations that require verified resistance, reactance, temperature, installation configuration, and power-factor data.
- NFPA 70, National Electrical CodeOfficial code source for jurisdiction-specific electrical requirements and voltage-drop context. Consult the edition adopted by the authority having jurisdiction.
- IAEI — Voltage Drop CalculationsPractical discussion of NEC voltage-drop references and the distinction between general design guidance and application-specific requirements.
- Turn2Engineering Voltage Drop CalculatorCompanion single-scenario calculator and internal method reference.
Dataset and Review Details
- Publisher
- Turn2Engineering
- Calculation basis
- 2KIL/CM and √3KIL/CM
- Default K values
- Copper 12.9; aluminum 21.2 ohm-cmil/ft, used as simplified design constants
- Length convention
- One-way input
- Conductor range
- 18 AWG through 1000 kcmil; metric area shown as an approximate conversion
- Rights status
- Original calculated comparison; restricted standards tables excluded
- Known exclusions
- Temperature-adjusted AC impedance, harmonics, parallel runs, motor starting, nonlinear loads
- Review label
- Generated engineering reference; project review not claimed
Voltage Drop Calculation Table FAQs
Enter the one-way distance from source to load. The table applies a factor of 2 for a two-wire or single-phase path and √3 for a balanced three-phase calculation.
No. Three percent is widely used as design guidance for many branch circuits, but the controlling requirement depends on the application, equipment, locally adopted code edition, and authority having jurisdiction.
A conductor may carry the current thermally yet lose too much voltage over a long run. The final size must satisfy both voltage-drop performance and all applicable ampacity and installation rules.
For a balanced three-phase line-to-line calculation, the phase relationships produce the √3 multiplier. A two-wire or single-phase loop uses the outgoing-and-return factor of 2.
Detailed AC calculations can include conductor temperature, AC resistance, reactance, power factor, raceway configuration, harmonics, and other effects that the simplified K-factor method does not model.
Use the Table as a Preliminary Comparison
Start with the actual source voltage, expected current, one-way distance, circuit type, material, and design target. Use the first qualifying row as a voltage-drop screening result, then complete the independent ampacity and installation checks required for the project.