What is the amp rating for 8 gauge wire?

Use 44 A for 8 AWG copper on equipment with 75 °C terminations, which covers most breakers and panel lugs. Read 37 A instead when the conductor is inside NM-B cable, and treat 49 A as the derating base only. Aluminium of the same size is about 34 A at 75 °C.

What breaker size goes with 8 AWG copper?

The largest standard overcurrent device that 8 AWG copper supports at 75 °C is 40 A. For a continuous load, the load itself must not exceed 80% of that rating.

What is the diameter of 8 AWG wire?

The bare conductor is 0.1285 inches (3.264 mm) in diameter, which is 16,510 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 0.216 inches.

What is the resistance of 8 AWG wire?

About 0.6282 ohms per 1000 feet for copper and 1.0297 ohms per 1000 feet for aluminium, at 75 °C.

How far can I run 8 AWG wire?

Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 8 AWG copper stays under 3% voltage drop for about 115 feet one-way. Doubling the voltage roughly doubles the allowable distance.

8 AWG Wire — Amp Rating, Ampacity & Diameter

Ampacity, geometry, resistance, conduit fill and maximum run length for 8 AWG conductors in copper and aluminium.

Quick answer

8 AWG copper carries about 44 A at 75 °C (37 A at 60 °C, 49 A at 90 °C). The bare conductor is 0.1285 in (3.26 mm) and 16,510 circular mils, with 0.6282 Ω per 1000 ft. It pairs with a 40 A breaker at 75 °C terminations.

Copper 75 °C

44A

Aluminium 75 °C

34A

Diameter

0.1285in

Circular mils

16,510

Full specification

Size designation	8 AWG
AWG gauge number	8
Circular mils	16,510
kcmil	16.51
Bare diameter (in)	0.1285
Bare diameter (mm)	3.264
Cross-section (mm²)	8.37
THHN/THWN-2 OD (in)	0.216
Insulated area (sq in)	0.0366
Copper resistance (Ω/1000 ft)	0.6282
Aluminium resistance (Ω/1000 ft)	1.0297
Max standard breaker (Cu, 75 °C)	40 A

Published standardFormula estimate

Ampacity with derating

Estimated ampacity from the 90 °C column at various ambient temperatures and conductor counts.

Conductors in raceway	30 °C ambient	40 °C ambient	50 °C ambient	60 °C ambient
3	49 A	45 A	40 A	35 A
6	39 A	36 A	32 A	28 A
9	34 A	31 A	28 A	24 A
15	25 A	22 A	20 A	17 A
25	22 A	20 A	18 A	16 A

Source & method: The governing value is also capped by the termination rating, commonly 75 °C, which for this size is 44 A. Run your own conditions.

Maximum run length at 3% voltage drop

One-way distance for 8 AWG copper before drop exceeds 3%.

Load	120 V 1Ø	240 V 1Ø	208 V 3Ø	480 V 3Ø
10 A	230 ft	460 ft	461 ft	1,064 ft
15 A	153 ft	307 ft	307 ft	709 ft
20 A	115 ft	230 ft	230 ft	532 ft
30 A	76 ft	153 ft	153 ft	354 ft
40 A	57 ft	115 ft	115 ft	266 ft
50 A	46 ft	92 ft	92 ft	212 ft

Calculate your exact run

How many 8 AWG conductors fit in conduit

Maximum count of this size alone, at the fill percentage matching the resulting count.

Conduit	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
EMT	3	5	9	16	22	36	63	96	126	161
IMC	3	6	10	17	24	39	56	86	115	148
RMC	3	5	9	16	22	37	53	81	109	140
PVC Sch 40	3	5	9	15	21	35	51	79	106	137
PVC Sch 80	1	4	7	13	18	31	44	70	94	122

Mix conductor sizes in the fill calculator

8 AWG copper ampacity vs aluminium ampacity

Ampacity by conductor material and insulation temperature rating, at 30 °C ambient with no more than three current-carrying conductors.

Material	60 °C (TW, NM-B)	75 °C (THW, THWN, XHHW)	90 °C (THHN, THWN-2, XHHW-2)
Copper	37 A	44 A	49 A
Aluminium	29 A	34 A	39 A

The 8 AWG copper ampacity figure you use on a real circuit is the 75 °C column, 44 A, because breakers and lugs on most equipment are listed for 75 °C even when the conductor insulation is rated 90 °C. The 90 °C value, 49 A, is the starting point for ambient and conductor-count derating only — you derate from 90 °C, then cap the answer at the termination rating.

Aluminium of the same size carries roughly 77% of the copper value (34 A at 75 °C), so an aluminium feeder is normally stepped up one to two sizes to match a copper circuit. NM-B cable is always read from the 60 °C column regardless of the temperature stamped on the conductor insulation.

Source & method: Values are model estimates from conductor geometry and resistivity — see methodology and verify against the NEC edition enforced locally.

Neighbouring sizes

Compare 8 AWG with the sizes immediately above and below it before sizing a circuit.

Smaller10 AWG32 A copper at 75 °C · 0.1019" diameter Larger6 AWG59 A copper at 75 °C · 0.1620" diameter

Size	Cu 75 °C	Al 75 °C	Diameter (in)	Circular mils
12 AWG	24 A	19 A	0.0808	6,530
10 AWG	32 A	25 A	0.1019	10,383
8 AWG (this page)	44 A	34 A	0.1285	16,510
6 AWG	59 A	46 A	0.1620	26,251
4 AWG	80 A	62 A	0.2043	41,741

Circuits that use 8 AWG

Breaker ratings whose smallest copper conductor at 75 °C terminations is 8 AWG.

8 AWG amp rating, diameter and metric equivalent

The amp rating for 8 AWG wire depends on the insulation temperature rating, not on the conductor alone. Copper ampacity is about 37 A on a 60 °C conductor, 44 A at 75 °C and 49 A at 90 °C, all at 30 °C ambient with no more than three current-carrying conductors in the raceway. The carrying capacity drops from there in hot spaces or crowded conduit, and terminations rated 75 °C cap what you can actually use.

Geometrically, 8 AWG is 0.1285 in (3.26 mm) in bare diameter, which is 16,510 circular mils. The cross sectional area works out to 8.37 mm², so the nearest IEC 60228 metric conductor is the next standard size at or above that figure — AWG sizes and mm² sizes never line up exactly, so round up rather than to the closest value.

American Wire Gauge (AWG) is a standard specification for the sizes of solid round wires used as electrical conductors, and the AWG number counts the drawing operations used to reach the diameter. That is why larger gauges are thinner wire and why standardized wire steps follow a fixed ratio: one AWG step changes diameter by about 12.2% and area by about 26%. Above 1 AWG the American standard continues 1/0 to 4/0, then switches to kcmil for anything larger.

Where 8 AWG actually gets used

8 AWG covers 40 to 50 A work: ranges and cooktops on smaller installations, Level 2 EV chargers at 32 A continuous, hot tubs and spa panels, welders, and feeders to detached garage subpanels. At this size the conductor is nearly always stranded and pulled as THHN/THWN-2 in raceway or as SER/SE cable rather than NM-B.

The 75 °C termination limit dominates from here up. The 90 °C insulation rating on the conductor is a derating base only — the breaker lug, the panel bus and the appliance terminal block are what cap the usable ampacity, which is why the 75 °C column is the number that appears on nearly every 8 AWG installation drawing.

Frequently asked

How many amps can 8 AWG wire carry?: 8 AWG copper is estimated at 37 A at 60 °C, 44 A at 75 °C and 49 A at 90 °C, at 30 °C ambient with no more than three current-carrying conductors. Aluminium of the same size is about 34 A at 75 °C.
What is the amp rating for 8 gauge wire?: Use 44 A for 8 AWG copper on equipment with 75 °C terminations, which covers most breakers and panel lugs. Read 37 A instead when the conductor is inside NM-B cable, and treat 49 A as the derating base only. Aluminium of the same size is about 34 A at 75 °C.
What breaker size goes with 8 AWG copper?: The largest standard overcurrent device that 8 AWG copper supports at 75 °C is 40 A. For a continuous load, the load itself must not exceed 80% of that rating.
What is the diameter of 8 AWG wire?: The bare conductor is 0.1285 inches (3.264 mm) in diameter, which is 16,510 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 0.216 inches.
What is the resistance of 8 AWG wire?: About 0.6282 ohms per 1000 feet for copper and 1.0297 ohms per 1000 feet for aluminium, at 75 °C.
How far can I run 8 AWG wire?: Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 8 AWG copper stays under 3% voltage drop for about 115 feet one-way. Doubling the voltage roughly doubles the allowable distance.