How many amps can 8 gauge wire carry?

8 AWG copper is rated 40 A (60 °C), 50 A (75 °C) and 55 A (90 °C), and goes on a breaker of up to 40 A in NM-B cable or 50 A with 75 °C terminations.

8 AWG wire ampacity

8 AWG copper and aluminum ampacity at 60, 75 and 90 °C, up to three current-carrying wires at 30 °C (86 °F) ambient, with the largest breaker at 75 °C
Rating	Copper	Aluminum
60 °C, NM-B	40 A	35 A
75 °C	50 A	40 A
90 °C	55 A	45 A
Max breaker, 75 °C	50 A	40 A

Copper
Aluminum

8 AWG ampacity by temperature rating.

8 AWG wire size and resistance

8 AWG bare conductor size and copper resistance at operating temperature. The diameter is the nominal AWG value; stranded wire of the same size is slightly larger.
Diameter, AWG nominal	0.1285 in. / 3.26 mm
Area	16,510 cmil / 8.37 mm²
Copper resistance	0.781 Ω per 1,000 ft

How far can 8 AWG wire run?

Longest one-way 8 AWG copper run within 3% voltage drop, at the full 50 A breaker load and at half load, at 120 and 240 V
Load	120 V	240 V
50 A	46 ft	92 ft
25 A	92 ft	184 ft

How many 8 AWG wires fit in conduit

Maximum number of 8 AWG THHN wires by conduit type and trade size, at 40% fill for three or more wires
THHN in	1/2″	3/4″	1″
EMT	3	6	9
PVC Sch 40	3	5	9
PVC Sch 80	1	4	7
RMC	3	6	9

What 8 AWG wire is used for

Cooktops and wall ovens
Air conditioners and heat pumps

Check a 8 AWG circuit

What are you sizing for?

Breaker or load

One-way distance

From the panel to the load, not there and back

Voltage

Conductor

Termination rating

Result

8 AWG copper

Ampacity sets the size; the voltage drop is within 3%.

Breaker: 40 A
Voltage drop: 3.1 V (1.3%)
Volts at the load: 236.9 V
Ground wire: 10 AWG copper

How it is calculated

Breaker: 40 A rounded up to a standard size = 40 A.
Smallest copper conductor rated for 40 A at 60 °C: 8 AWG.
Drop = 2 × K × 40 A × 50 ft ÷ 16,510 cmil = 3.13 V, target 3% of 240 V.

Sources

7 published documents, checked on 2026-11-13

NFPA 70, National Electrical Code (2023): Allowable ampacities of insulated conductors, Table 310.16
NFPA 70, National Electrical Code (2023): Overcurrent protection of small conductors, Section 240.4(D)
NFPA 70, National Electrical Code (2023): Conductor properties, Chapter 9 Table 8
NFPA 70, National Electrical Code (2023): Ampacity of flexible cords and cables, Table 400.5(A)(1)
NFPA 70, National Electrical Code (2023): Percent of cross section of conduit and tubing for conductors, Chapter 9 Table 1
NFPA 70, National Electrical Code (2023): Dimensions and percent area of conduit and tubing, Chapter 9 Table 4
NFPA 70, National Electrical Code (2023): Dimensions of insulated conductors, Chapter 9 Table 5

Compared with 13 published documents, last on 2026-11-13

American Wire Group (edition not stated): Allowable Ampacities of Insulated Aluminum or Copper-Clad Aluminum Conductors — Aluminum columns and the 15/25 A aluminum small-conductor limits
Carlon / Thomas & Betts (ABB) (catalog (edition not stated)): General information: wire fill based on Chapter 9 Table 1 — Conduit fill percentages
Cerrowire (NEC 2017): Ampacity Charts — Copper 60/75/90 °C and aluminum 75/90 °C, 14 AWG to 600 kcmil
Florida International University (course notes, NEC edition not stated): Chapter III, Electrical Wiring Components (Figure 3.18, area of THHN conductors) — THHN areas for 14 to 6 AWG; the larger sizes match a training reproduction of the same table
LugsDirect (NEC 2020): Ampacities of Insulated Conductors From NEC Table 310.16 — All columns, copper and aluminum, every size on this site
LugsDirect (AWG formula): AWG Wire Chart, kcmil and Metric Wire Sizes — Circular mils, square millimeters and diameters by size
Michigan State University, Biosystems and Agricultural Engineering (NEC edition not stated): Electrical Tech Note 212: Conductor Properties — Conductor area, dc resistance at 75 °C and the K constants
Omni Cable (NEC 2017): NEC Ampacity Data — All columns, copper and aluminum
Southwire Company, Power Cable Installation Guide (2005 (cites 2005 NEC)): Dimensions and percent area of conduit and tubing, Table 8 (EMT, rigid PVC Schedule 40 and 80) — Fill percentages and internal areas of EMT, PVC Schedule 40 and Schedule 80
Southwire (NEC 2023): SPEC 10003, THHN/THWN-2 building wire — 14–10 AWG copper and the 15/20/30 A small-conductor limits
Southwire (NEC 2023): SPEC 45007, aluminum XHHW-2 building wire — Copper small-conductor limits 15/20/30 A
Southwire (NEC 2023): SPEC 70126, SJOOW portable cord — Cord ampacity, 18–10 AWG, two current-carrying conductors
Wheatland Tube (2022): Rigid Metal Conduit Submittal Sheet, weights and dimensions — Rigid metal conduit inside diameters; the areas follow from them

Calculated by Calculate.diy with the method of the National Electrical Code® (NEC®), 2023 edition; not the NEC text. Methodology. For planning only: check local code and use a licensed electrician.