Wire Gauge Calculator
Find the wire size you need for a circuit. Enter the voltage, load and length of the run; the calculator checks both how much current each gauge can carry and how much voltage is lost over the distance.
| Gauge | Diameter | Ampacity | Voltage drop | Drop % | Voltage at load |
|---|
Red values fail the requirement. The highlighted row is the smallest wire that passes both checks.
How to choose the right wire size
- Enter the circuit voltage and the load in amps or watts, and choose AC single phase, three phase or DC.
- Enter the one-way distance from the panel or battery to the load, and the maximum voltage drop you will accept (3% is the usual target).
- Read the recommended gauge. The table shows every size, with failing values in red, so you can see whether the current or the distance is deciding the size.
Two checks: ampacity and voltage drop
Ampacity is the current a wire can carry without overheating. The values here come from the US National Electrical Code (NEC) Table 310.16, with the small-conductor limits of section 240.4(D): 14 AWG copper on a 15 A breaker, 12 AWG on 20 A and 10 AWG on 30 A. NM-B cable used in most homes is limited to the 60 °C column; individual THHN wires in conduit with 75 °C terminals can use the 75 °C column.
Voltage drop is the voltage lost in the wire itself because of its resistance. Over a long run it can leave motors struggling, lights dim and electronics misbehaving, and the lost energy turns into heat. The NEC recommends keeping branch circuits under 3% and the total of feeder and branch under 5%. Drop is calculated from the NEC Chapter 9, Table 8 resistances: twice the one-way length for single-phase and DC, or √3 times for three phase.
Low-voltage DC wiring
At 12 or 24 volts, voltage drop is usually what decides the size. A 20 A load 15 feet from a 12 V battery loses about 1.2 V on 12 AWG wire, nearly 10%; it takes 8 AWG to keep the drop under 4%. That is why RV, marine and solar wiring often uses much thicker cable than household wiring for the same current. Always fuse low-voltage wiring close to the battery.
Common wire sizes
| Copper size | Usual breaker | Typical uses |
|---|---|---|
| 14 AWG | 15 A | Lighting, general outlets |
| 12 AWG | 20 A | Kitchen, bathroom and garage outlets |
| 10 AWG | 30 A | Water heater, dryer, small AC |
| 8 AWG | 40 A | Range, cooktop |
| 6 AWG | 50–60 A | EV charger, range, subpanel |
Safety: this calculator is a planning aid. Local codes, ambient temperature, bundling several cables, conduit fill and equipment instructions can all require a larger wire. Electrical work can be dangerous; have it inspected and, where required, done by a licensed electrician.
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Frequently asked questions
What is AWG?
American Wire Gauge, the US system for wire sizes. Smaller numbers are thicker wires: 10 AWG is thicker than 14 AWG. Sizes larger than 1 AWG are written 1/0, 2/0, 3/0 and 4/0.
Should I measure the length one way or round trip?
Enter the one-way distance from the source to the load. The calculator accounts for the current flowing out and back.
Can I use aluminum wire?
Yes, for larger feeders it is common and cheaper, but it needs to be about two sizes larger than copper and must be used with connectors rated for aluminum.
Why is the recommended size bigger than the breaker chart?
Because the run is long. The breaker chart covers overheating only; voltage drop over distance often needs a thicker wire.
Is anything sent to a server?
No. Everything is calculated in your browser, and nothing you enter leaves your device.