Interactive electrical engineering reference

Wire Ampacity Chart

Look up copper and aluminum conductor ampacity, apply supported ambient-temperature and conductor-count factors, and see the governing preliminary limit.

Base condition: 30°C ambient
Temperature columns: 60°C · 75°C · 90°C
Materials: Copper · aluminum
Use: Preliminary reference

JavaScript enables the preliminary derating calculator, filters, sorting, and copy actions. The server-rendered wire ampacity chart and engineering guidance remain available below.

Preliminary adjustment tool

Check Adjusted Wire Ampacity

Base ampacity × ambient factor × conductor-count factor, capped by the applicable temperature-column limit.

Example: 6 AWG copper with 90°C insulation, 75°C terminations, 36–40°C ambient, and 4–6 current-carrying conductors gives 75 A × 0.91 × 0.80 = 54.6 A before other code checks.

Base reference values

Copper and Aluminum Wire Ampacity Chart

Insulated conductors rated 0–2,000 V, not more than three current-carrying conductors in a raceway, cable, or earth, at 30°C ambient.

Filter by material, show one temperature column or all three, or search a designation such as “6 AWG” or “250 kcmil.”

Ampacity in amperes for copper and aluminum or copper-clad aluminum insulated conductors under the stated base conditions.
		Ampacity by conductor temperature rating			Action
					Action
14 AWG	Copper	15 A	20 A	25 A
12 AWG	Copper	20 A	25 A	30 A
10 AWG	Copper	30 A	35 A	40 A
8 AWG	Copper	40 A	50 A	55 A
6 AWG	Copper	55 A	65 A	75 A
4 AWG	Copper	70 A	85 A	95 A
3 AWG	Copper	85 A	100 A	115 A
2 AWG	Copper	95 A	115 A	130 A
1 AWG	Copper	110 A	130 A	145 A
1/0 AWG	Copper	125 A	150 A	170 A
2/0 AWG	Copper	145 A	175 A	195 A
3/0 AWG	Copper	165 A	200 A	225 A
4/0 AWG	Copper	195 A	230 A	260 A
250 kcmil	Copper	215 A	255 A	290 A
300 kcmil	Copper	240 A	285 A	320 A
350 kcmil	Copper	260 A	310 A	350 A
400 kcmil	Copper	280 A	335 A	380 A
500 kcmil	Copper	320 A	380 A	430 A
600 kcmil	Copper	350 A	420 A	475 A
750 kcmil	Copper	400 A	475 A	535 A
1000 kcmil	Copper	455 A	545 A	615 A
12 AWG	Aluminum / Cu-clad Al	15 A	20 A	25 A
10 AWG	Aluminum / Cu-clad Al	25 A	30 A	35 A
8 AWG	Aluminum / Cu-clad Al	30 A	40 A	45 A
6 AWG	Aluminum / Cu-clad Al	40 A	50 A	55 A
4 AWG	Aluminum / Cu-clad Al	55 A	65 A	75 A
3 AWG	Aluminum / Cu-clad Al	65 A	75 A	85 A
2 AWG	Aluminum / Cu-clad Al	75 A	90 A	100 A
1 AWG	Aluminum / Cu-clad Al	85 A	100 A	115 A
1/0 AWG	Aluminum / Cu-clad Al	100 A	120 A	135 A
2/0 AWG	Aluminum / Cu-clad Al	115 A	135 A	150 A
3/0 AWG	Aluminum / Cu-clad Al	130 A	155 A	175 A
4/0 AWG	Aluminum / Cu-clad Al	150 A	180 A	205 A
250 kcmil	Aluminum / Cu-clad Al	170 A	205 A	230 A
300 kcmil	Aluminum / Cu-clad Al	195 A	230 A	260 A
350 kcmil	Aluminum / Cu-clad Al	210 A	250 A	280 A
400 kcmil	Aluminum / Cu-clad Al	225 A	270 A	305 A
500 kcmil	Aluminum / Cu-clad Al	260 A	310 A	350 A
600 kcmil	Aluminum / Cu-clad Al	285 A	340 A	385 A
750 kcmil	Aluminum / Cu-clad Al	320 A	385 A	435 A
1000 kcmil	Aluminum / Cu-clad Al	375 A	445 A	500 A

Important: These are base reference values, not automatic breaker sizes or final conductor selections. The 90°C column may be usable for permitted correction and adjustment calculations, but lower terminal, equipment, conductor-protection, or application-specific limits may govern.

More filters and table actions

Bulk CSV export is intentionally unavailable because the underlying NEC/NFPA table is rights-sensitive. Copy one limited row summary and consult the official standard for authoritative project use.

Scope boundary

When This Wire Ampacity Chart Applies

Not installation approval

This educational reference does not determine compliance for a specific circuit. Confirm the locally adopted NEC edition, local amendments, wiring method, insulation, terminal markings, equipment instructions, conductor-count rules, ambient conditions, and special application provisions.

Base table conditions

The chart addresses insulated copper and aluminum or copper-clad aluminum conductors rated 0–2,000 V, with not more than three current-carrying conductors in a raceway, cable, or directly buried, at 30°C ambient. A different table or method may be required for free air, flexible cords, medium-voltage conductors, cable tray, rooftop exposure, direct sunlight, parallel conductors, or manufacturer-controlled assemblies.

Why the highest number may not govern

A 90°C insulation rating does not automatically permit the 90°C table value as the final circuit ampacity. The higher column may be the starting point for allowed corrections and adjustments, while 60°C or 75°C terminations, equipment limitations, or conductor-protection rules impose the final cap.

Selection path

How to Use the Wire Ampacity Chart

Confirm scope. Make sure the actual conductor and installation fall within the table conditions.
Find material and size. Copper and aluminum have different ampacity values for the same designation.
Choose the permitted temperature column. Use conductor insulation, terminal markings, equipment limitations, and applicable code rules.
Apply both thermal factors when required. Ambient correction and current-carrying-conductor adjustment address different heat effects.
Apply the lowest governing limit. Compare the adjusted value with the applicable terminal/equipment column and all other code limitations.

Core calculation

Adjusted ampacity = base ampacity × ambient-temperature factor × conductor-count factor

The result must still be compared with the applicable terminal, equipment, conductor-protection, and special-application limits.

Ambient-temperature bands used by the tool

Temperature correction factors used by the preliminary calculator.
Ambient	60°C	75°C	90°C
≤10°C	1.29	1.20	1.15
11–15°C	1.22	1.15	1.12
16–20°C	1.15	1.11	1.08
21–25°C	1.08	1.05	1.04
26–30°C	1.00	1.00	1.00
31–35°C	0.91	0.94	0.96
36–40°C	0.82	0.88	0.91
41–45°C	0.71	0.82	0.87
46–50°C	0.58	0.75	0.82
51–55°C	0.41	0.67	0.76
56–60°C	—	0.58	0.71
61–65°C	—	0.47	0.65
66–70°C	—	0.33	0.58
71–75°C	—	—	0.50
76–80°C	—	—	0.41

Current-carrying-conductor bands used by the tool

Adjustment factors used by the preliminary calculator.
Current-carrying conductors	Factor
1–3	1.00
4–6	0.80
7–9	0.70
10–20	0.50
21–30	0.45
31–40	0.40
41 or more	0.35

Do not assume every conductor in a raceway or cable is counted identically. Equipment grounding conductors are not normally current carrying, and neutral treatment depends on the circuit configuration and applicable rules.

Worked checks

Wire Ampacity Calculation Examples

12 AWG copper with 60°C terminations

Given: 90°C insulation, 30°C ambient, three current-carrying conductors, and 60°C terminals.

Method: The 90°C base is 30 A. Both factors are 1.00, but the 60°C column is 20 A.

Preliminary result: 20 A governs. Small-conductor protection rules and equipment markings still require verification.

6 AWG copper in a hotter raceway

Given: 90°C insulation, 75°C terminals, 36–40°C ambient, and six current-carrying conductors.

Method: 75 A × 0.91 × 0.80 = 54.6 A.

Preliminary result: 54.6 A is below the 75°C-column cap of 65 A, so the thermal adjustments govern this simplified check.

Engineering context

Ampacity, Breaker Size, and Voltage Drop Are Different Checks

Ampacity: The conductor’s allowable current under defined thermal and installation conditions.

Breaker or fuse size: The protective-device rating selected under load, equipment, conductor-protection, and code rules.

Voltage drop: The voltage reduction caused by conductor impedance and circuit length; it may require a larger conductor.

Design current: The current the conductor and protective system must serve after applicable load factors are applied.

Common mistakes to avoid

Using the 90°C value as the final ampacity without checking terminations.
Treating a table value as an automatic breaker-size recommendation.
Applying ambient correction but forgetting conductor-count adjustment, or vice versa.
Confusing conduit fill with the number of current-carrying conductors.
Ignoring voltage drop, equipment instructions, or special rules for motors, HVAC, EV charging, PV, services, feeders, welders, and parallel conductors.

Wire Ampacity Chart Engineering References

NEC conductor ampacity reference · AWG, kcmil, and amperes · Wire Ampacity Reference 2.0

This page uses a transformed educational presentation of commonly referenced conductor ampacity values and code concepts. The official NFPA publication and the edition adopted by the authority having jurisdiction remain controlling for project work.

NFPA 70, National Electrical CodePrimary source basis for conductor ampacity tables, conductor temperature limits, ambient correction, adjustment factors, and related requirements.
International Association of Electrical Inspectors: Reorganization of NEC Article 310Explanatory context for Article 310 organization and ampacity terminology.
UL Solutions Wire and Cable Application GuideProduct-marking and conductor temperature-rating context for listed wire and cable.

Dataset and Source-Check Details

Edition basis: 2023 NEC educational basis; verify the locally adopted edition and amendments
Evidence scope: Table 310.16 conditions, common conductor sizes, 60°C/75°C/90°C columns, temperature correction, and conductor-count adjustment
Source-controlled fields: Base ampacity values and discrete correction/adjustment factors
Calculated fields: Adjusted ampacity and the lower temperature-column comparison shown by the preliminary tool
Known exclusions: Alternate wiring methods, special applications, equipment-specific rules, local amendments, and project approval
Rights and download: Limited educational transformation; no bulk NEC-derived CSV distribution
Source checked: August 9, 2026
Publisher: Turn2Engineering

Wire Ampacity Chart FAQs

How many amps can 12-gauge wire carry?

The base 12 AWG copper values shown are 20 A at 60°C, 25 A at 75°C, and 30 A at 90°C. The permitted application can be lower because terminal ratings, small-conductor protection, wiring method, insulation, ambient temperature, conductor count, equipment rules, and local code still govern.

Why are three amp ratings shown for one wire size?

Can the 90°C ampacity be used for THHN conductors?

Does wire ampacity decrease in hot locations?

Is wire ampacity the same as breaker size?

Wire Ampacity Chart Summary

Start with the correct material, size, and temperature column; apply required ambient and conductor-count factors; then use the lowest applicable terminal, equipment, conductor-protection, or special-rule limitation. The calculator exposes that simplified calculation path, while the server-rendered chart keeps the base lookup available without JavaScript.

Complete conductor selection also requires the adopted code, overcurrent protection, voltage drop, equipment instructions, special application rules, available fault current, and local amendments.