4 AWG Wire — Amp Rating, Ampacity & Diameter
Ampacity, geometry, resistance, conduit fill and maximum run length for 4 AWG conductors in copper and aluminium.
Quick answer
Copper 75 °C
80A
Aluminium 75 °C
62A
Diameter
0.2043in
Circular mils
41,741
Full specification
| Size designation | 4 AWG |
|---|---|
| AWG gauge number | 4 |
| Circular mils | 41,741 |
| kcmil | 41.74 |
| Bare diameter (in) | 0.2043 |
| Bare diameter (mm) | 5.189 |
| Cross-section (mm²) | 21.15 |
| THHN/THWN-2 OD (in) | 0.324 |
| Insulated area (sq in) | 0.0824 |
| Copper resistance (Ω/1000 ft) | 0.2485 |
| Aluminium resistance (Ω/1000 ft) | 0.4073 |
| Max standard breaker (Cu, 75 °C) | 80 A |
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 | 90 A | 82 A | 73 A | 64 A |
| 6 | 72 A | 66 A | 59 A | 51 A |
| 9 | 63 A | 58 A | 51 A | 45 A |
| 15 | 45 A | 41 A | 37 A | 32 A |
| 25 | 41 A | 37 A | 33 A | 29 A |
Source & method: The governing value is also capped by the termination rating, commonly 75 °C, which for this size is 80 A. Run your own conditions.
Maximum run length at 3% voltage drop
One-way distance for 4 AWG copper before drop exceeds 3%.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 10 A | 582 ft | 1,164 ft | 1,165 ft | 2,690 ft |
| 15 A | 388 ft | 776 ft | 777 ft | 1,793 ft |
| 20 A | 291 ft | 582 ft | 582 ft | 1,345 ft |
| 30 A | 194 ft | 388 ft | 388 ft | 896 ft |
| 40 A | 145 ft | 291 ft | 291 ft | 672 ft |
| 50 A | 116 ft | 232 ft | 233 ft | 538 ft |
How many 4 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 | 1 | 2 | 4 | 7 | 9 | 16 | 28 | 42 | 56 | 71 |
| IMC | 1 | 2 | 4 | 7 | 10 | 17 | 24 | 38 | 51 | 66 |
| RMC | 1 | 2 | 4 | 7 | 10 | 16 | 23 | 36 | 48 | 62 |
| PVC Sch 40 | 1 | 1 | 4 | 7 | 9 | 15 | 22 | 35 | 47 | 60 |
| PVC Sch 80 | 1 | 1 | 3 | 6 | 8 | 13 | 19 | 31 | 42 | 54 |
4 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 | 68 A | 80 A | 90 A |
| Aluminium | 53 A | 62 A | 70 A |
The 4 AWG copper ampacity figure you use on a real circuit is the 75 °C column, 80 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, 90 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 78% of the copper value (62 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 4 AWG with the sizes immediately above and below it before sizing a circuit.
Circuits that use 4 AWG
Breaker ratings whose smallest copper conductor at 75 °C terminations is 4 AWG.
4 AWG amp rating, diameter and metric equivalent
The amp rating for 4 AWG wire depends on the insulation temperature rating, not on the conductor alone. Copper ampacity is about 68 A on a 60 °C conductor, 80 A at 75 °C and 90 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, 4 AWG is 0.2043 in (5.19 mm) in bare diameter, which is 41,741 circular mils. The cross sectional area works out to 21.15 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 4 AWG sits: the first feeder-only size
4 AWG is the smallest conductor that is used almost exclusively as a feeder or service conductor rather than a branch circuit. In copper it is the common 100 A dwelling service and main-feeder conductor under the service allowance; in aluminium it is the usual 70 to 80 A subpanel feeder. Branch circuits this large are rare because there is no ordinary receptacle or appliance in that range.
It is also the last size that a competent installer can still terminate comfortably by hand. Compression lugs, split bolts and mechanical set-screw lugs all appear at 4 AWG, and a torque screwdriver becomes standard rather than optional. Above this size the crimp tool and the hydraulic head take over, which changes cost and labour more than the conductor price does.
For raceway planning, 4 AWG THHN is roughly the point where three conductors plus a ground stop fitting 3/4 inch tubing and 1 inch becomes the practical minimum. Voltage drop is usually not the binding constraint on a 100 A residential service at typical lateral lengths, but on a 250 ft rural run it can force 2 AWG on drop alone.
Frequently asked
- How many amps can 4 AWG wire carry?
- 4 AWG copper is estimated at 68 A at 60 °C, 80 A at 75 °C and 90 A at 90 °C, at 30 °C ambient with no more than three current-carrying conductors. Aluminium of the same size is about 62 A at 75 °C.
- What is the amp rating for 4 gauge wire?
- Use 80 A for 4 AWG copper on equipment with 75 °C terminations, which covers most breakers and panel lugs. Read 68 A instead when the conductor is inside NM-B cable, and treat 90 A as the derating base only. Aluminium of the same size is about 62 A at 75 °C.
- What breaker size goes with 4 AWG copper?
- The largest standard overcurrent device that 4 AWG copper supports at 75 °C is 80 A. For a continuous load, the load itself must not exceed 80% of that rating.
- What is the diameter of 4 AWG wire?
- The bare conductor is 0.2043 inches (5.189 mm) in diameter, which is 41,741 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 0.324 inches.
- What is the resistance of 4 AWG wire?
- About 0.2485 ohms per 1000 feet for copper and 0.4073 ohms per 1000 feet for aluminium, at 75 °C.
- How far can I run 4 AWG wire?
- Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 4 AWG copper stays under 3% voltage drop for about 291 feet one-way. Doubling the voltage roughly doubles the allowable distance.
Related charts & calculators
- Allen Wrench Size ChartHex key sizes with SAE and metric cross-reference.
- Voltage Drop CalculatorPercent drop, end voltage and minimum conductor for any run length.
- Conduit Fill CalculatorFill percentage and maximum conductor count for EMT, RMC, IMC and PVC.
- Breaker Size CalculatorOvercurrent device rating and minimum conductor from load current.
- Wire Ampacity CalculatorDerated ampacity for ambient temperature and bundled conductors.
- Box Fill CalculatorVolume allowances for conductors, clamps, devices and grounds per NEC 314.16.