Wire Size Calculator - AWG Wire Gauge Finder
Find the recommended AWG wire gauge from current, voltage, wire length, and maximum voltage drop, using a standard ampacity table.
Recommended Wire Gauge
12 AWG
Allowed drop: 3.60 V | Required: 1.800 Ω/1000ft
How to Size a Wire Gauge (AWG)
Choosing the right wire gauge involves two checks: the wire must be rated to safely carry the circuit's current (ampacity), and it must be thick enough that resistance over the run length doesn't cause an excessive voltage drop. This calculator computes the maximum resistance per 1,000 ft that keeps voltage drop under your target percentage, then finds the smallest standard AWG size from the reference table below that satisfies both the resistance and ampacity requirements.
AWG Reference Table (Copper Wire)
| AWG | Resistance (Ω/1000ft) | Typical Ampacity (A) |
|---|---|---|
| 14 | 2.525 | 15 |
| 12 | 1.588 | 20 |
| 10 | 0.999 | 30 |
| 8 | 0.628 | 40 |
| 6 | 0.395 | 55 |
| 4 | 0.249 | 70 |
| 3 | 0.197 | 85 |
| 2 | 0.156 | 95 |
| 1 | 0.124 | 110 |
| 1/0 | 0.098 | 125 |
| 2/0 | 0.078 | 145 |
| 3/0 | 0.062 | 165 |
| 4/0 | 0.049 | 195 |
Example
A 20A, 120V circuit running 50 feet one-way with a 3% max voltage drop allows a drop of 120 × 0.03 = 3.6V. The required resistance is (3.6 × 1000) ÷ (2 × 50 × 20) = 1.8 Ω/1000ft. Looking at the table, 12 AWG (1.588 Ω/1000ft, 20A ampacity) satisfies both requirements, so 12 AWG is recommended.
Common Use Cases
- Sizing extension cords or long circuit runs for tools, generators, or workshops.
- Planning wiring for a garage, shed, or outbuilding a significant distance from the main panel.
- Checking whether an existing wire run is adequate for a new higher-draw appliance.
FAQs
Is this a substitute for professional electrical code compliance?
No. This calculator gives a reasonable engineering estimate based on standard resistance and ampacity figures, but actual wire sizing must follow your local electrical code (such as the NEC), which accounts for insulation type, ambient temperature, conduit fill, and other derating factors. Always consult a licensed electrician for real installations.
Why does wire length matter so much?
Voltage drop increases with the round-trip distance current has to travel, so doubling the length of a circuit run doubles the voltage drop for the same wire and current, often requiring a thicker gauge to compensate.
What voltage drop percentage should I use?
3% is a commonly recommended maximum for branch circuits, and 5% for the combined feeder and branch circuit, though some equipment or codes may specify a different limit.