NEC wire ampacity chart & derating calculator

NEC 2023 Table 310.16 ampacity for copper and aluminum at 60, 75 and 90 °C, with derating. 6 AWG copper is 55 A as NM-B cable but 65 A as THHN on 75 °C terminals. Nine 12 AWG THHN in one raceway at 40 °C drop from 30 A to 19.1 A.

Drawing at true size…

02 · Ampacity · NEC 2023 Table 310.16

6 AWG copper · 90 °C insulation, 75 °C terminals, 30 °C, 3 conductors

USE:

6 AWG COPPER · 65 A ALLOWABLE · 60 A MAX BREAKER

Allowable

65 A

6 AWG Cu

Max breaker

60 A

ampacity ≥ breaker

For your load

8 AWG

50 A

6 AWG copper carries 75 A after derating from the 90 °C column and 65 A at its 75 °C terminals, so it is good for 65 A on a breaker up to 60 A.

Meets NEC 2023 Table 310.16 at 75°C — verify with your local AHJ/inspector110.14(C)
Load 50 A ≤ 65 A310.14

Derating math

Table 310.16 at 90 °C: 75 Aderating starts at the insulation rating
Ambient factor: × 1.0030 °C, Table 310.15(B)(1)
Bundling factor: × 1.003 current-carrying conductors, 310.15(C)(1)
Derated: 75 A
Terminal limit (75 °C): 65 A110.14(C)
Allowable: 65 Athe terminals decide

6 AWG

Copper 60 / 75 / 90 °C: 55 / 65 / 75 ANM-B uses the 60 °C column (334.80)
Aluminum 60 / 75 / 90 °C: 40 / 50 / 55 A
Largest breaker (Cu, 75 °C): 60 Aampacity ≥ breaker
Solid diameter: 0.162"4.12 mm · ASTM B258 formula
Stranded (7 strands): 0.184"4.67 mm · Table 8
THHN outside: 0.254"6.45 mm · 0.0507 in² · Table 5
Area: 26,240 cmil13.30 mm² · nearest IEC 16 mm²
DC resistance, 75 °C: 0.491 Ω/1000 ftaluminum 0.808 Ω/1000 ft · Table 8
Copper weight: 79.4 lb/1000 ft

NEC ampacity tables 58 rows

Sort any column, print a shop sheet, download CSV. Click a row to load it in the calculator.

NEC Table 310.16 ampacity, copper

18 rows

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NEC 2023 Table 310.16 allowable ampacity of insulated copper conductors at 60, 75 and 90 °C, with the largest standard breaker each may take (240.4(D) small-conductor caps, ampacity at least the breaker rating)

15	20	25	15	14 AWG
20	25	30	20	12 AWG
30	35	40	30	10 AWG
40	50	55	50	10 AWG
55	65	75	60	10 AWG
70	85	95	80	8 AWG
85	100	115	100	8 AWG
95	115	130	110	6 AWG
110	130	145	125	6 AWG
125	150	170	150	6 AWG
145	175	195	175	6 AWG
165	200	225	200	6 AWG
195	230	260	225	4 AWG
215	255	290	250	4 AWG
240	285	320	250	4 AWG
260	310	350	300	4 AWG
280	335	380	300	4 AWG
320	380	430	350	3 AWG

Values agree across Elliott Electric (2020 NEC), Cerrowire (2017 NEC) and Southwire SPEC 10028 (2023 NEC). NEC 2026 adds 16 AWG copper and 14 AWG copper-clad aluminum rows.

NEC Table 310.16 ampacity, aluminum

17 rows

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NEC 2023 Table 310.16 allowable ampacity of insulated aluminum conductors at 60, 75 and 90 °C, with the largest standard breaker each may take (240.4(D) small-conductor caps, ampacity at least the breaker rating)

15	20	25	15	12 AWG
25	30	35	25	10 AWG
35	40	45	40	8 AWG
40	50	55	50	8 AWG
55	65	75	60	8 AWG
65	75	85	70	6 AWG
75	90	100	90	6 AWG
85	100	115	100	6 AWG
100	120	135	110	4 AWG
115	135	150	125	4 AWG
130	155	175	150	4 AWG
150	180	205	175	4 AWG
170	205	230	200	4 AWG
195	230	260	225	2 AWG
210	250	280	250	2 AWG
225	270	305	250	2 AWG
260	310	350	300	2 AWG

Values agree across Elliott Electric (2020 NEC), Cerrowire (2017 NEC) and Southwire SPEC 10028 (2023 NEC). NEC 2026 adds 16 AWG copper and 14 AWG copper-clad aluminum rows.

Ambient temperature correction, Table 310.15(B)(1)

16 rows

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NEC Table 310.15(B)(1) correction factors for ambient temperatures other than 30 °C (86 °F), for 60, 75 and 90 °C conductors

50 or less	1.29	1.20	1.15
52–59	1.22	1.15	1.12
61–68	1.15	1.11	1.08
70–77	1.08	1.05	1.04
79–86	1.00	1.00	1.00
88–95	0.91	0.94	0.96
97–104	0.82	0.88	0.91
106–113	0.71	0.82	0.87
115–122	0.58	0.75	0.82
124–131	0.41	0.67	0.76
133–140	—	0.58	0.71
142–149	—	0.47	0.65
151–158	—	0.33	0.58
160–167	—	—	0.50
169–176	—	—	0.41
178–185	—	—	0.29

More than three current-carrying conductors, Table 310.15(C)(1)

7 rows

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NEC Table 310.15(C)(1) adjustment factors for more than three current-carrying conductors in a raceway or cable longer than 24 inches
			Actions
	100 %	30 A
	80 %	24 A
	70 %	21 A
	50 %	15 A
	45 %	13.5 A
	40 %	12 A
	35 %	10.5 A

Grounding conductors are not counted (310.15(F)); a neutral carrying only unbalanced current is not counted (310.15(E)).

05 / Field guide

One table,
three temperatures.

NEC Table 310.16 lists the current a conductor may carry with no more than three current-carrying conductors in a raceway or cable at 30 °C. Every size has a 60 °C, 75 °C and 90 °C column, and which one you may use depends on the insulation, the wiring method and the weakest termination. The calculator applies them in that order.

Derate from 90 °C, stop at the terminals

Correction for a hot attic or a crowded conduit starts from the insulation’s own column (90 °C for THHN), so the derating has some headroom. The result is then capped at the column of the terminations, which 110.14(C) sets at 60 °C for circuits of 100 A or less unless the equipment is marked 75 °C (most breakers and lugs today are marked 60/75 °C).

Example: nine 12 AWG THHN in one conduit in a 40 °C space: 30 A × 0.91 × 0.70 = 19.1 A, below the 25 A terminal limit, so 19.1 A it is: a 15 A breaker, or 20 A only where the 240.4(B) next-size-up rule applies.

allowable = min( 310.16[insulation °C] × ambient factor × bundling factor , 310.16[terminal °C] )

Small-conductor caps

240.4(D) caps the breaker on small copper no matter what the table says: 14 AWG 15 A, 12 AWG 20 A, 10 AWG 30 A (and 12 AWG aluminum 15 A, 10 AWG aluminum 25 A).

240.4(B) lets a conductor whose ampacity is not a standard breaker size take the next size up, up to 800 A, except on multi-outlet receptacle circuits: 6 AWG NM-B (55 A) may go on a 60 A breaker.

NEC 2026

The 2026 edition adds rows for 16 AWG copper and 14 AWG copper-clad aluminum to Table 310.16 (310.5(A) lowers the minimum sizes) and moves the load calculations from Article 220 to Article 120. Building-wire ampacities are unchanged; this site cites NEC 2023, the edition most jurisdictions enforce.

Worked example: a 40 A circuit through a hot attic

8 AWG THHN copper is 55 A at 90 °C. In a 50 °C attic the ambient factor for the 90 °C column is 0.82, so it carries 45.1 A, still under its 50 A terminal limit: the allowable is 45.1 A and a 40 A breaker is fine. The same 8 AWG as NM-B starts from the same 55 A for derating but is capped at the 60 °C column, 40 A. Run more than three current-carrying conductors through the same attic and the bundling factor stacks on top.

Questions

Answered plainly.

What is the ampacity of 10 AWG copper?

30 A at 60 °C, 35 A at 75 °C and 40 A at 90 °C, but 240.4(D) limits it to a 30 A breaker. As NM-B cable it is 30 A.

Why is NM-B limited to 60 °C?

NEC 334.80 sets the ampacity of NM cable at the 60 °C column, even though its conductors are rated 90 °C. The 90 °C rating may be used only as the starting point for derating.

How much does aluminum carry compared with copper?

About 78 %. 1 AWG aluminum is 100 A at 75 °C against 130 A for copper, which is why aluminum feeders run a size or two larger.

When do I derate for more than three wires?

When more than three current-carrying conductors share a raceway or cable longer than 24 inches: 4–6 conductors 80 %, 7–9 70 %, 10–20 50 % (Table 310.15(C)(1)). Grounds do not count, and a neutral carrying only the unbalanced current does not count.

What is a continuous load?

A load that runs three hours or more, like an EV charger, a spa heater or store lighting. The circuit must be sized for 125 % of it (210.19(A)(1), 215.2(A)(1)).

Which edition of the NEC does this use?

NEC 2023, with notes where NEC 2026 changes a row. Your jurisdiction adopts an edition, sometimes with amendments; check with the local inspector.

NEC wire ampacity chart & derating calculator

Derating math

6 AWG

NEC ampacity tables 58 rows

NEC Table 310.16 ampacity, copper

NEC Table 310.16 ampacity, aluminum

Ambient temperature correction, Table 310.15(B)(1)

More than three current-carrying conductors, Table 310.15(C)(1)

One table,three temperatures.

Derate from 90 °C, stop at the terminals

Small-conductor caps

NEC 2026

Worked example: a 40 A circuit through a hot attic

Answered plainly.

What is the ampacity of 10 AWG copper?

Why is NM-B limited to 60 °C?

How much does aluminum carry compared with copper?

When do I derate for more than three wires?

What is a continuous load?

Which edition of the NEC does this use?

Browse all 20 gauges, 12 conduit sizes and 10 circuits

One table,
three temperatures.