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Ampacity Chart

Allowable current by conductor size at each insulation rating, with live ambient temperature and bundling adjustment.

Quick answer

For copper at 75 °C and 30 °C ambient: 14 AWG ≈ 18 A, 12 AWG ≈ 24 A, 10 AWG ≈ 32 A, 8 AWG ≈ 44 A, 6 AWG ≈ 59 A, 4 AWG ≈ 80 A. Hotter ambient temperatures and more than three bundled conductors both reduce these numbers.

Adjust to see the derated columns update. 30 °C and three conductors is the un-derated baseline.

Copper ampacity by size

Base values at 30 °C ambient with three current-carrying conductors, plus the derated result at 30 °C with 3 conductors.

Size60 °C75 °C90 °CDerated (30 °C, 3 cond.)
18 AWG8 A10 A11 A11 A
16 AWG11 A13 A15 A15 A
14 AWG15 A18 A20 A20 A
12 AWG20 A24 A27 A27 A
10 AWG27 A32 A37 A37 A
8 AWG37 A44 A49 A49 A
6 AWG50 A59 A67 A67 A
4 AWG68 A80 A90 A90 A
3 AWG79 A93 A105 A105 A
2 AWG92 A108 A122 A122 A
1 AWG107 A126 A142 A142 A
1/0 AWG124 A146 A165 A165 A
2/0 AWG144 A170 A192 A192 A
3/0 AWG168 A198 A223 A223 A
4/0 AWG195 A230 A260 A260 A
250 kcmil217 A257 A289 A289 A
300 kcmil245 A289 A326 A326 A
350 kcmil271 A319 A360 A360 A
400 kcmil295 A348 A393 A393 A
500 kcmil341 A403 A454 A454 A
600 kcmil384 A454 A511 A511 A
750 kcmil444 A524 A591 A591 A
Sizes 18 AWG through 750 kcmil. Derated column uses the 90 °C insulation rating, the normal starting point for THHN/THWN-2.
Formula estimate — source: Power-law ampacity model, calibrated against standard practice

Source & method: Method and calibration error are documented on the methodology page. Conductor geometry is computed from the ASTM B258 AWG formula.

Copper versus aluminium at the same load

Target loadCopperAluminium
15 A14 AWG12 AWG
20 A12 AWG10 AWG
30 A10 AWG8 AWG
40 A8 AWG6 AWG
50 A6 AWG4 AWG
60 A4 AWG4 AWG
70 A4 AWG3 AWG
90 A3 AWG1 AWG
100 A2 AWG1/0 AWG
125 A1 AWG2/0 AWG
150 A2/0 AWG3/0 AWG
175 A3/0 AWG4/0 AWG
200 A4/0 AWG250 kcmil
Smallest size that carries the target current at 75 °C, 30 °C ambient.

Ampacity is only half the sizing question. On long runs voltage drop usually governs — check the run with the voltage drop calculator.

Frequently asked

What is ampacity?
Ampacity is the maximum current a conductor can carry continuously without exceeding its insulation temperature rating. It depends on conductor size and material, insulation rating, ambient temperature and how many conductors are bundled together.
How many amps can 12 AWG copper carry?
12 AWG copper is estimated at 20 A at 60 °C, 24 A at 75 °C and 27 A at 90 °C, before ambient or bundling derating. In practice 12 AWG is used on 20 A branch circuits.
Why is aluminium ampacity lower than copper?
Aluminium has about 61% of copper's conductivity, so the same cross-section carries roughly 78% of the current for the same temperature rise. Aluminium conductors are typically sized one to two steps larger than copper for the same load.
Does the 90 °C column mean I can load the wire to that value?
No. The 90 °C column is used for derating calculations. The final ampacity is limited by the temperature rating of the terminations, which is commonly 75 °C on equipment rated over 100 A and 60 °C on some smaller devices.
Is this the same as the NEC ampacity table?
No. Code tables are copyrighted, so these values come from a published physics model calibrated against standard practice. They track within a few percent for common sizes, but the adopted code is the legal authority and must be checked before installation.

Gear for load and ampacity checks

Gear for load and ampacity checks

Measure the real load before you trust a table.

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