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Wire Gauge Chart
Quick answer: AWG runs backwards — lower number, thicker wire. 14 AWG for 15 A, 12 AWG for 20 A, 10 AWG for 30 A in standard residential branch circuits. On long runs, voltage drop forces a larger conductor before ampacity does.
AWG diameters, areas and copper ampacity alongside the residential circuits each size serves — plus the voltage-drop limits that actually govern long runs.
American Wire Gauge (AWG) chart
AWG runs backwards: the smaller the number, the thicker the wire. The scale is geometric — each three-gauge step roughly doubles the cross-sectional area, and each six-gauge step roughly doubles the diameter.
| AWG | Diameter (in) | Diameter (mm) | Area (kcmil) | Ampacity 60°C | Ampacity 75°C |
|---|---|---|---|---|---|
| 14 | 0.0641 | 1.628 | 4.1 | 15 | 20 |
| 12 | 0.0808 | 2.053 | 6.5 | 20 | 25 |
| 10 | 0.1019 | 2.588 | 10.4 | 30 | 35 |
| 8 | 0.1285 | 3.264 | 16.5 | 40 | 50 |
| 6 | 0.1620 | 4.115 | 26.3 | 55 | 65 |
| 4 | 0.2043 | 5.189 | 41.7 | 70 | 85 |
| 3 | 0.2294 | 5.827 | 52.6 | 85 | 100 |
| 2 | 0.2576 | 6.544 | 66.4 | 95 | 115 |
| 1 | 0.2893 | 7.348 | 83.7 | 110 | 130 |
Ampacity figures are for copper conductors per NEC Table 310.16 at an ambient of 30°C with no more than three current-carrying conductors in a raceway. Aluminium conductors carry roughly 78% of these values.
Common residential circuits
| Wire | Breaker | Typical circuit |
|---|---|---|
| 14 AWG | 15 A | General lighting, bedroom receptacles |
| 12 AWG | 20 A | Kitchen and bathroom receptacles, garage |
| 10 AWG | 30 A | Electric dryer, water heater, small A/C |
| 8 AWG | 40 A | Electric range, larger A/C |
| 6 AWG | 55 A | Large range, sub-panel feeder |
Residential branch circuits are commonly sized to the 60°C column regardless of the cable’s own rating, because the terminations on standard breakers and devices are rated 60°C or 75°C. The lowest-rated component in the path governs.
Voltage drop is the constraint on long runs
Ampacity governs short runs; on long ones voltage drop usually forces a larger conductor first. The usual target is no more than 3% drop on a branch circuit.
For a single-phase circuit: Vdrop = (2 × L × R × I) ÷ 1000, where L is one-way length in feet, R is resistance in ohms per 1,000 ft, and I is the current in amps. Copper resistance is roughly 3.07 Ω/1000 ft at 14 AWG, 1.93 at 12, 1.21 at 10 and 0.764 at 8.
| Wire | Load | Max one-way run for 3% drop at 120 V |
|---|---|---|
| 14 AWG | 15 A | ~39 ft |
| 12 AWG | 20 A | ~47 ft |
| 10 AWG | 30 A | ~50 ft |
| 12 AWG | 20 A at 240 V | ~93 ft |
This is why a detached garage or a shed at the end of a long run needs conductors well above what the breaker size alone would suggest.
Copper vs aluminium
Aluminium conductors carry roughly 78% of copper’s ampacity at the same gauge, so an aluminium feeder is typically sized two gauges larger. Aluminium is still standard for large service entrance and feeder conductors because of cost and weight, but it requires terminations rated for it (marked AL or CU-AL) and an antioxidant compound at connections.
Frequently asked questions
What gauge wire for a 20 amp circuit?
12 AWG copper. 14 AWG is limited to 15 amps and putting it on a 20 amp breaker is a fire hazard, because the breaker will not trip before the conductor overheats.
Is a higher AWG number thicker or thinner?
Thinner. The scale runs backwards — 14 AWG is thinner than 12 AWG, which is thinner than 10. Each three-gauge step roughly doubles the cross-sectional area.
How far can I run 12 gauge wire on a 20 amp circuit?
About 47 feet one-way at 120 V before voltage drop exceeds the usual 3% target, and roughly double that at 240 V. Ampacity is not the limit on long runs — voltage drop is, and it forces a larger conductor first.
Can I use aluminium wire instead of copper?
For feeders and service entrance conductors, yes, and it is common. Aluminium carries about 78% of copper's ampacity at the same gauge, so it is usually sized two gauges larger, and it requires terminations rated AL or CU-AL plus an antioxidant compound. It is not used for standard branch-circuit wiring in modern residential work.