8 AWG Wire — Ampacity, Conduit Fill & Dimensions

Everything the code tables say about 8 AWG conductors on one page: ampacity by temperature rating, breaker limits, conduit fill, physical size, resistance and voltage-drop distances.

8 AWG copper carries 40 A at 60°C, 50 A at 75°C and 55 A at 90°C.

Copper, 75°C

50 A

Aluminum, 75°C

40 A

Conductor area

16,510 cmil · 8.37 mm²

THHN diameter

0.216 in

DC resistance, Cu

0.778 Ω/1000 ft

8 AWG ampacity

8 AWG ampacity (amps), 30°C ambient, not more than three current-carrying conductors
	Copper			Aluminum
Installation	60°C	75°C	90°C	60°C	75°C	90°C
Raceway, cable or earth — Table 310.16	40	50	55	35	40	45
Single conductor in free air — Table 310.17	60	70	80	45	55	60

Typical use: 40–50 A circuits: ranges, cooktops, 40 A EV chargers and small sub-panel feeders.

Use the column that matches the lowest temperature rating in the circuit — usually the 75°C terminations on breakers and lugs. The 90°C column is a starting point for derating, not a rating you can load the wire to. NM-B (Romex) cable is always limited to the 60°C column.

As a copper equipment grounding conductor, 8 AWG is the minimum for circuits protected at up to 100 A; in aluminum, up to 60 A. See the grounding conductor table.

8 AWG conduit fill

How many 8 AWG THHN wires fit in conduit (40% fill)
Conduit	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	4"
EMT	3	6	9	16	22	36	64	96	161
PVC Schedule 40	3	5	9	16	21	36	51	79	137
PVC Schedule 80	1	4	7	13	18	31	45	70	123
Rigid Metal Conduit	3	6	9	16	22	37	53	82	140
IMC	3	6	10	18	24	39	56	86	149
Flexible Metal Conduit	3	6	9	14	20	35	53	77	137
Liquidtight Flexible Metal Conduit	3	6	9	16	21	35	53	81	138
ENT	3	5	9	16	21	36	—	—	—

Mixing sizes or using another insulation? Use the conduit fill calculator.

8 AWG dimensions

8 AWG overall diameter and area including insulation
Insulation	Diameter (in)	Diameter (mm)	Area (in²)	Area (mm²)
THHN, THWN, THWN-2	0.216	5.49	0.0366	23.6
XHHW, XHHW-2, XHH	0.236	5.99	0.0437	28.2
TW, THW, THHW, THW-2	0.236	5.99	0.0437	28.2
RHH, RHW, RHW-2 (with outer covering)	0.326	8.28	0.0835	53.9

8 AWG voltage drop

Maximum one-way length of 8 AWG copper for 3% voltage drop
Load	120 V 1-phase	240 V 1-phase	208 V 3-phase	480 V 3-phase
15 A	154 ft	308 ft	308 ft	712 ft
20 A	115 ft	231 ft	231 ft	534 ft
30 A	77 ft	154 ft	154 ft	356 ft
40 A	57 ft	115 ft	115 ft	267 ft
50 A	46 ft	92 ft	92 ft	213 ft

Based on 0.778 Ω per 1000 ft for stranded copper at 75°C (1.28 Ω for aluminum). For other loads and lengths use the voltage drop calculator.

All wire sizes

Frequently asked questions

How many amps can 8 AWG wire carry?

8 AWG copper is rated 40 A at 60°C, 50 A at 75°C and 55 A at 90°C when run in conduit or cable. Aluminum is rated 35, 40 and 45 A. Most terminations are rated 75°C, so the 75°C figure is the one normally used.

What size conduit do I need for 8 AWG wire?

Three 8 AWG THHN conductors need at least 1/2-inch EMT. 1/2-inch EMT holds 3 and 3/4-inch holds 6.

What is the diameter of 8 AWG wire?

The bare conductor is 16,510 circular mils (8.37 mm²). With THHN insulation the overall diameter is about 0.216 in (5.49 mm) and the area is 0.0366 in², which is the figure used for conduit fill.

How far can I run 8 AWG wire?

For a 3% voltage drop on a 240 V single-phase circuit carrying 50 A, about 92 feet one way in copper. Halve that at 120 V. Lighter loads go proportionally farther.

NECTables.com is an independent reference and is not affiliated with, endorsed by, or a substitute for the National Fire Protection Association (NFPA). NEC® and National Electrical Code® are registered trademarks of the NFPA. Values shown are commonly published engineering data and independent calculations based on the methods of NFPA 70; they are not a reproduction of the Code. Always confirm against the edition adopted in your jurisdiction, including local amendments, and consult a licensed electrician or engineer before doing electrical work.