NEC Wire Size Chart: Complete Ampacity Reference

Every AWG wire size has a maximum current it can safely carry — its ampacity — set by NEC Table 310.16. The table below is the 75°C column, which covers the most common building-wire insulation types (THHN, THWN-2) for up to three current-carrying conductors in a raceway or cable. It's the reference this site's calculators are built on.

AWG	Circular mils	Copper (75°C)	Aluminum (75°C)
14	4,110	20A	— (not rated)
12	6,530	25A	20A
10	10,380	35A	30A
8	16,510	50A	40A
6	26,240	65A	50A
4	41,740	85A	65A
3	52,620	100A	75A
2	66,360	115A	90A
1	83,690	130A	100A
1/0	105,600	150A	120A
2/0	133,100	175A	135A
3/0	167,800	200A	155A
4/0	211,600	230A	180A
250 kcmil	250,000	255A	205A
300 kcmil	300,000	285A	230A
350 kcmil	350,000	310A	250A
400 kcmil	400,000	335A	270A
500 kcmil	500,000	380A	310A

Why this is the 75°C column specifically

Table 310.16 actually has three temperature columns — 60°C, 75°C, and 90°C — corresponding to different insulation ratings. 75°C (THHN/THWN-2 in wet locations, or most general building wire in practice) is the one most calculators and most residential/commercial branch-circuit work reference. The 90°C column allows higher ampacity for the same wire, but the terminals it connects to (breakers, lugs) are very often only rated for 60°C or 75°C — so the equipment, not the wire, usually ends up being the limiting factor. Don't assume you can use the 90°C ampacity just because the wire insulation supports it.

When this table alone isn't enough

This is the base ampacity table — several NEC-required adjustments can lower the usable ampacity below what's listed here, and none of them are captured by AWG size alone:

• More than 3 current-carrying conductors in a raceway requires a derating factor (NEC 310.15(C)(1)).
• Ambient temperature above 30°C (86°F) — attics, rooftops, hot climates — also requires derating.
• Continuous loads (running 3+ hours, like most HVAC or lighting) require sizing the circuit at 125% of the load per NEC 210.19(A).

None of the tools on this site apply these adjustment factors automatically — they work from the base table. For anything beyond a straightforward, short, well-ventilated run, that's exactly the kind of judgment call worth getting a licensed electrician to confirm.