Wire Gauge Calculator
Calculate the recommended AWG wire gauge based on current, distance, and acceptable voltage drop.
Supports feet and meters.
Wire gauge selection determines whether a cable can safely carry a given electrical current over a given distance without overheating or wasting excessive power through voltage drop.
The AWG system (American Wire Gauge): AWG numbers run counterintuitively — a lower AWG number means a thicker wire. AWG 4 is much thicker than AWG 14. Each three-step decrease in AWG roughly doubles the wire’s cross-sectional area and halves its resistance.
Voltage drop formula:
V_drop = (2 × L × I × R) ÷ 1000
Variable definitions:
- V_drop = voltage lost along the wire (volts)
- L = one-way cable length (feet)
- I = current load (amperes)
- R = wire resistance (ohms per 1,000 feet, from AWG table)
- × 2 = accounts for the round-trip (positive and return conductors)
AWG copper wire reference table:
| AWG | Ω/1000 ft | Max Amps (in conduit) |
|---|---|---|
| 14 | 2.525 | 15 A |
| 12 | 1.588 | 20 A |
| 10 | 0.999 | 30 A |
| 8 | 0.628 | 40 A |
| 6 | 0.395 | 55 A |
| 4 | 0.249 | 70 A |
| 2 | 0.156 | 95 A |
Worked example: A 20 A circuit runs 75 feet (one way) using AWG 12 wire: V_drop = (2 × 75 × 20 × 1.588) ÷ 1000 = 4.76 V On a 120 V circuit: 4.76 ÷ 120 = 3.97% voltage drop
Industry standards:
- ≤ 3% drop — recommended for branch circuits (NEC guideline)
- ≤ 5% total — maximum acceptable for feeder + branch combined
- Upgrade to AWG 10 in this example to bring drop under 3%
Aluminum wire note: Aluminum wire (common in older homes and service panels) has about 1.6× the resistance of copper. Always use the aluminum column of resistance tables when dealing with aluminum conductors.