Wire Size Calculator
Enter the current your load draws, the one-way distance from the panel and the supply voltage. The calculator picks the smallest AWG wire that carries the current safely and keeps voltage drop under your limit.
- AWG 14 to 4/0
- Copper or aluminium
- Ampacity and voltage drop
For North American AWG wiring. Always follow your local electrical code and have the work checked.
Two separate limits decide wire size. The wire has to carry the current without overheating, which is its ampacity. It also has to deliver enough voltage at the far end, which gets harder the longer the run. On short runs ampacity decides. On long runs voltage drop usually wins and pushes you up a size or two.
AWG wire sizes and ratings
Smaller AWG numbers mean thicker wire. Search for a gauge or amp rating.
| AWG | Diameter (mm) | Area (mm²) | Copper (A) | Aluminium (A) |
|---|---|---|---|---|
| 14 | 1.63 | 2.08 | 20 | – |
| 12 | 2.05 | 3.31 | 25 | 20 |
| 10 | 2.59 | 5.26 | 35 | 30 |
| 8 | 3.26 | 8.37 | 50 | 40 |
| 6 | 4.11 | 13.3 | 65 | 50 |
| 4 | 5.19 | 21.2 | 85 | 65 |
| 3 | 5.83 | 26.7 | 100 | 75 |
| 2 | 6.54 | 33.6 | 115 | 90 |
| 1 | 7.35 | 42.4 | 130 | 100 |
| 1/0 | 8.25 | 53.5 | 150 | 120 |
| 2/0 | 9.27 | 67.4 | 175 | 135 |
| 3/0 | 10.4 | 85 | 200 | 155 |
| 4/0 | 11.7 | 107 | 230 | 180 |
Ampacity values are for copper and aluminium at 75°C terminals from NEC table 310.16. Many breakers and devices are only rated for 60°C, which lowers 14, 12 and 10 AWG copper to 15, 20 and 30 amps.
Distance against voltage drop
The same 20 amp load on four wire gauges. Slide the run length and watch the voltage drop grow on each gauge.
Voltage drop doubles when distance doubles. That is why a garden workshop 150 feet from the house can need 6 AWG for a load that 12 AWG would handle inside.
How to size a wire
Work from the load to the wire. These are the same steps an electrician follows.
Find the load current
Read the nameplate. If it lists watts, divide by voltage. Continuous loads count at 125%.
The breaker protects the wire, not the appliance. Once you know the wire size, the breaker must be no larger than the wire's rating.
Copper or aluminium wire
Both are allowed, with different rules. Compare the two conductors.
Lower resistance, so a smaller size carries the same current. Easy to terminate on all standard devices.
About 61% of copper's conductivity, so it needs a larger size. Must use AL-rated lugs and anti-oxidant paste.
Aluminium is common for feeders and service entrances because it is cheaper and lighter. For branch circuits in a house, copper is almost always used.
Before you run the wire
Wire size is one part of a safe circuit. Tick these off as you plan.
Tick each item as you go.
If you are adding a circuit to a panel, check the panel has spare capacity and space. A licensed electrician can confirm the plan and handle the permit.
What the result covers
Every figure you need to choose a wire. Each tile explains one result.
The smallest standard size that meets both limits.
The current the wire can carry at 75°C.
Volts lost on the round trip, as volts and percent.
What your appliance actually receives.
Area in mm², for comparing with metric cable.
The calculator takes the larger of the two sizes, ampacity or voltage drop, so you get one answer that satisfies both.
Frequently Asked Questions
No question matches that search.
What size wire do I need for 20 amps?
12 AWG copper for runs up to about 50 feet at 120 V. Beyond that, voltage drop pushes you to 10 AWG.
What wire size for a 30 amp circuit?
10 AWG copper is the usual choice. For runs over about 80 feet at 240 V, check voltage drop and consider 8 AWG.
What gauge wire for 50 amps?
6 AWG copper at 75°C terminals, or 4 AWG aluminium. 8 AWG copper is rated 50 A but only at 75°C on both ends.
Does wire length affect wire size?
Yes. Longer runs lose more voltage. The calculator uses the one-way distance and doubles it for the return path.
Is 3% voltage drop the rule?
The NEC recommends 3% for a branch circuit and 5% total. It is guidance rather than a strict requirement, but it keeps motors and lights working well.
Can I use a bigger wire than needed?
Yes. Bigger wire runs cooler and drops less voltage. The only limits are cost, and whether it fits the terminals.
What is the difference between AWG and mm²?
AWG is a gauge number where smaller means thicker. mm² is the actual cross-sectional area. 12 AWG is about 3.31 mm².
Choose the wire, then the breaker
Find the load, measure the real cable route and let the calculator check both ampacity and voltage drop. Match the breaker to the wire you choose, follow local code, and get new circuits inspected.
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