NEC Wire Ampacity Calculator

Copper conductor ampacity from NEC Table 310.16 with temperature correction and conductor count derating. Free — no account required.

Wire & Conditions

Wire Size

Insulation Type

Auto-selects temperature column: 90°C / 194°F

Current-Carrying Conductors (default 3)

No derating (1–3 conductors)

Ambient Temperature (default 30°C / 86°F)

Ampacity Result

NEC Table 310.16 — Copper, 90°C / 194°F column

Adjusted Ampacity

30.0A

Step-by-step calculation

Step 1Base ampacity — 12 AWG, 90°C / 194°F column (NEC Table 310.16)

30 A

Step 2Ambient temperature correction factor — 30°C (86°F) × NEC Table 310.15(B)(2)(a)

× 1.00

After temp correction (30 × 1.00)= 30.00 A

Step 3Conductor count derating — 3 conductors (NEC Table 310.15(B)(3)(a))

× 100%

Final adjusted ampacity (30.00 × 1.00)= 30.0 A

NEC Table 310.16 — Quick Reference (Copper, 60/75/90°C)

Size	60°C	75°C	90°C
14 AWG	15*	20	25
12 AWG	20*	25	30
10 AWG	30	35	40
8 AWG	40	50	55
6 AWG	55	65	75
4 AWG	70	85	95
3 AWG	85	100	115
2 AWG	95	115	130
1 AWG	110	130	145
1/0 AWG	125	150	170
2/0 AWG	145	175	195
3/0 AWG	165	200	225
4/0 AWG	195	230	260
250 kcmil	215	255	290
300 kcmil	240	285	320
350 kcmil	260	310	350
400 kcmil	280	335	380
500 kcmil	320	380	430
600 kcmil	350	420	475
700 kcmil	385	460	520
750 kcmil	400	475	535
800 kcmil	410	490	555
900 kcmil	435	520	585
1000 kcmil	455	545	615

* Per NEC 240.4(D), overcurrent protection limited to 15A for 14 AWG, 20A for 12 AWG, 30A for 10 AWG.

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This calculator references NEC Table 310.16 values. Always verify with your local Authority Having Jurisdiction (AHJ) and the current NEC edition adopted in your jurisdiction. Values shown are for copper conductors only.