NEC Cable Ampacity

Allowable ampacities per NEC Table 310.16 for copper and aluminum conductors, with standard derating factors for temperature and conduit fill.

Table 310 16

Wire Size	Cu 60°C (TW,UF)	Cu 75°C (THW,THWN)	Cu 90°C (THHN,XHHW-2)	Al 60°C (TW,UF)	Al 75°C (THW,THWN)	Al 90°C (THHN,XHHW-2)
14 AWG	15	20	25	—	—	—
12 AWG	20	25	30	15	20	25
10 AWG	30	35	40	25	30	35
8 AWG	40	50	55	30	40	45
6 AWG	55	65	75	40	50	60
4 AWG	70	85	95	55	65	75
3 AWG	85	100	115	65	75	85
2 AWG	95	115	130	75	90	100
1 AWG	110	130	145	85	100	115
1/0	125	150	170	100	120	135
2/0	145	175	195	115	135	150
3/0	165	200	225	130	155	175
4/0	195	230	260	150	180	205
250 kcmil	215	255	290	170	205	230
300 kcmil	240	285	320	190	230	255
350 kcmil	260	310	350	210	250	280
400 kcmil	280	335	380	225	270	305
500 kcmil	320	380	430	260	310	350
600 kcmil	355	420	475	285	340	385
750 kcmil	400	475	535	320	385	435
1000 kcmil	455	545	615	375	445	500

Derating

AMBIENT TEMPERATURE CORRECTION — NEC 310.15(B)(1)

Ambient Temp (°F)	60°C Factor	75°C Factor	90°C Factor
70-77	1.08	1.04	1.04
78-86	1	1	1
87-95	0.91	0.96	0.96
96-104	0.82	0.91	0.91
105-113	0.71	0.87	0.87
114-122	0.58	0.82	0.82
123-131	0.41	0.76	0.76
132-140	—	0.71	0.71
CONDUIT FILL ADJUSTMENT — NEC 310.15(C)(1)
Number of Current-Carrying Conductors	Adjustment Factor
4-6	0.8
7-9	0.7
10-20	0.5
21-30	0.45
31-40	0.4
41+	0.35
DERATING CALCULATOR
Base ampacity (from Table 310.16)	100	A
Ambient temp correction factor	0.91	—
Conduit fill adjustment factor	0.8	—
Derated ampacity		A

Source: NEC_Cable_Ampacity_Reference_v1.xlsx

© 2026 Inflection Point Engineering, LLC. All rights reserved. The content of this page — including calculation methods, reference data, written analysis, interactive tools, and source code — is the intellectual property of Inflection Point Engineering, LLC and is protected under applicable copyright, trademark, and trade secret laws. Unauthorized reproduction, redistribution, modification, or derivative use in whole or in part is prohibited without prior written consent.

Disclaimer. This material is provided for informational and educational purposes only and does not constitute professional engineering advice. Calculations, reference data, and methodologies are based on published standards and accepted engineering practice but are not a substitute for engineering judgment, site-specific analysis, or review by a licensed Professional Engineer. Inflection Point Engineering, LLC makes no warranties, express or implied, regarding the accuracy, completeness, or fitness for a particular purpose of any content presented here, and shall not be liable for any direct, indirect, incidental, or consequential damages arising from its use. Users assume all risk associated with applying this content to real-world design, operations, or decisions.