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Reference chart

NEC Ampacity Chart

The four tables you need to size a conductor: base ampacity, ambient temperature correction, conductor-count adjustment and the termination limit. For a worked answer use the ampacity calculator.

Quick answer: common copper sizes

These are base values from the 90°C column, before the ambient and conductor-count factors. If the terminations are rated 75°C, the usable ampacity cannot exceed the 75°C column either. The lower of the corrected 90°C value and the termination limit is what the conductor may carry.

Copper sizeBase ampacity, 90°C75°C termination limit
14 AWG25 A20 A
12 AWG30 A25 A
10 AWG40 A35 A
8 AWG55 A50 A
6 AWG75 A65 A

1. Base ampacity

Taken from the allowable ampacity table for insulated conductors, by temperature rating.

copper

Size60°C75°C90°C
1415 A20 A25 A
1220 A25 A30 A
1030 A35 A40 A
840 A50 A55 A
655 A65 A75 A
470 A85 A95 A
385 A100 A115 A
295 A115 A130 A
1110 A130 A145 A
1/0125 A150 A170 A
2/0145 A175 A195 A
3/0165 A200 A225 A
4/0195 A230 A260 A
250215 A255 A290 A
300240 A285 A320 A
350260 A310 A350 A
400280 A335 A380 A
500320 A380 A430 A
600350 A420 A475 A
750400 A475 A535 A
1000455 A545 A615 A

aluminum

Size60°C75°C90°C
1215 A20 A25 A
1025 A30 A35 A
835 A40 A45 A
640 A50 A55 A
455 A65 A75 A
365 A75 A85 A
275 A90 A100 A
185 A100 A115 A
1/0100 A120 A135 A
2/0115 A135 A150 A
3/0130 A155 A175 A
4/0150 A180 A205 A
250170 A205 A230 A
300195 A230 A260 A
350210 A250 A280 A
400225 A270 A305 A
500260 A310 A350 A
600285 A340 A385 A
750320 A385 A435 A
1000375 A445 A500 A

2. Ambient temperature correction

Multiply the base ampacity by the factor for the ambient temperature and the conductor temperature rating.

Ambient range (°C)60°C conductor75°C conductor90°C conductor
10 or less1.291.201.15
11–151.221.151.12
16–201.151.111.08
21–251.081.051.04
26–301.001.001.00
31–350.910.940.96
36–400.820.880.91
41–450.710.820.87
46–500.580.750.82
51–550.410.670.76
56–60—0.580.71
61–65—0.470.65
66–70—0.330.58
71–75——0.50
76–80——0.41
81–85——0.29

3. Conductor-count adjustment

Conductors in racewayFactor
1–31.00
4–60.80
7–90.70
10–200.50
21–300.45
31–400.40
41+0.35

4. Termination limit

The corrected ampacity does not settle it: terminations cap the usable ampacity as well. Circuits of 100 A or less are limited to the 60°C column unless the terminals and conductor are listed for 75°C; above 100 A the 75°C column applies.

Worked example

6 AWG copper, 90°C insulation, 40°C ambient, six current-carrying conductors in the raceway and 75°C terminations. The whole chain, with the clause behind each step.

StepValueClause
Base ampacity (90°C)75 ANEC 310.16
Ambient temperature correction (40°C)0.91NEC Table 310.15(B)(1)(1)
Adjustment for 6 conductors in raceway0.8NEC 310.15(C)(1)
Adjusted ampacity75 x 0.91 x 0.8 = 54.6 A—
Termination temperature limit (75°C)65 ANEC 110.14(C)
Final allowable ampacity (lower of the two)54.6 A—
Largest overcurrent device this conductor can protect50 ANEC 240.4; next-higher exception not assumed

The base value is 75 A; the ambient and conductor-count factors bring it to 54.6 A; the 75°C terminations allow 65 A. The lower of the two is the final allowable ampacity: 54.6 A. Run your own numbers in the ampacity calculator.

Frequently asked

How do the four tables fit together?
Start with the base ampacity for the conductor size and its insulation temperature rating. Multiply by the ambient correction factor, then by the conductor-count factor. Finally cap the result at the termination value in the column for the terminations you have (NEC 110.14(C)). The lower of the corrected value and the termination value is what the conductor may actually carry.
Which temperature column should I start from?
The insulation rating of the conductor. A 90°C conductor starts in the 90°C column, but that is a starting point only: if the terminations are rated 75°C, the usable ampacity is limited to the 75°C value for that size regardless of the insulation.
Does the ambient correction apply indoors?
It applies wherever the raceway runs. The base table assumes a 30°C ambient, so a mechanical room, a roof, an attic or an insulated wall that sits above that needs the matching factor. Use the temperature the conductors actually see, not the outdoor design temperature.
What counts as a current-carrying conductor?
Only current-carrying conductors drive the count adjustment. Whether a neutral counts depends on the circuit, and an equipment grounding conductor never counts here even though it does count for conduit fill. The ampacity calculator applies the factor to the number you enter.
Why is my result lower than the chart value?
Because the tables on this page are base values before correction. Once the ambient factor or the conductor-count factor is applied, and the termination column is checked, the usable number is usually lower than the column value that caught your eye.

Related pages

Cite this page

Use this reference in a report, article, course note or dataset. Calculated examples use this site's engine; reference data and explanatory text have separate sources and review status.

ElecCalcs. “NEC Ampacity Chart.” Updated October 29, 2026. https://eleccalcs.com/nec-ampacity-chart

Values reflect NEC 2023 and are pending review. Cite the edition you verified against.

Tables reflect NEC 2023 and are pending review. Educational use only — verify before construction.