Wire gauge chart: AWG sizes, amps and mm²

Wire size chart by amps (copper and aluminum)

This chart shows the maximum breaker or load for common conductors in a typical residential setting: copper or aluminum, THHN/THWN-2 or NM cable, with terminations rated 75 °C. Small copper wires are limited by NEC 240.4(D) — 14 AWG to 15 A, 12 AWG to 20 A and 10 AWG to 30 A — even though their table ampacity is higher.

This chart is for planning. Bundling, hot attics, conduit fill and local amendments can require a larger wire. Electrical work must meet your local code and is often required to be done or inspected by a licensed electrician.

AWG to mm² conversion

Outside North America wires are sized by cross-section in square millimetres. AWG sizes do not line up exactly with metric sizes, so always round up to the next metric size.

How distance changes the wire size

Every foot of wire has resistance, so the voltage at the end of a long run is lower than at the panel. The NEC recommends keeping voltage drop under 3 % on a branch circuit and 5 % for feeder plus branch. On short runs the amp chart decides the size; past roughly 50–75 ft at full load, voltage drop usually takes over.

Example: a 20 A load on 120 V, 100 ft away. 12 AWG copper is rated for 20 A, but it drops 7.72 V — 6.43%. 10 AWG brings it to 4.03% and 8 AWG to 2.55%, so the wire size calculator recommends 8 AWG.

Voltage drop for 20 A on 12 AWG copper at 120 V

At 240 V the same current drops the same number of volts, but that is only half the percentage — one reason long runs to pumps, shops and EV chargers are wired at 240 V.

Copper or aluminum?

Aluminum conducts about 61 % as well as copper, so it must be roughly two sizes larger for the same current. It is lighter and much cheaper, which is why it is standard for service entrances and large feeders. For branch circuits, copper is the norm; if you use aluminum, every lug and device must be rated AL/CU and the connections torqued to spec.

Common circuits and the wire they need

• General lighting, 15 A: 14 AWG copper (12 AWG on long runs).
• Kitchen counter and bathroom outlets, 20 A: 12 AWG copper.
• Electric water heater (4,500 W at 240 V, 18.75 A load): 10 AWG on a 30 A breaker.
• Clothes dryer, 30 A: 10 AWG copper.
• Electric range, 40–50 A: 8 AWG (40 A) or 6 AWG (50 A) copper.
• Level 2 EV charger, 48 A continuous on a 60 A breaker: 6 AWG copper THHN in conduit (4 AWG if you use NM cable).
• 100 A sub-panel: 3 AWG copper or 1 AWG aluminum feeders (check the panel and distance).

How many wires fit in a conduit?

Conduit fill is limited to 40 % of the inside area when there are three or more conductors. ¾ in EMT holds up to 16 conductors of 12 AWG THHN and 10 of 10 AWG. Use the conduit fill calculator for other combinations — and remember that more than three current-carrying wires in one raceway must be derated.

Extension cords and low-voltage wiring

The same rules apply to cords: a thin cord on a heavy load gets hot and drops voltage. Common guidance for extension cords is 16 AWG for up to 13 A on cords up to 50 ft, 14 AWG for 15 A, and 12 AWG for 20 A loads or runs of 100 ft. Never run a cord coiled on its reel under full load.

Low-voltage DC systems — 12 V solar, RV and boat wiring, landscape lighting — are far more sensitive. Ten amps on 12 AWG over a 20 ft one-way run drops 0.77 V, which is 6.43% of 12 V. That is why 12 V circuits often use 8–4 AWG wire for currents that a 120 V circuit would carry on 14 AWG. Enter your own voltage in the voltage drop calculator to check.

Checklist before you pull wire

1. Find the load current (nameplate amps, or watts ÷ volts) and the breaker size.
2. Measure the one-way length from the panel to the load, adding the vertical runs.
3. Pick the size from the ampacity chart, then check voltage drop for the length.
4. Check the conduit fill and derating if several circuits share a raceway.
5. Confirm the terminal temperature rating of the breaker and the device (60 °C or 75 °C).

How to read a wire gauge

AWG numbers go down as the wire gets thicker: 10 AWG is thicker than 14 AWG. Every 3 gauges roughly doubles the cross-section, and every 6 gauges doubles the diameter. Above 1 AWG the sizes continue as 1/0, 2/0, 3/0 and 4/0 (“one aught” to “four aught”), then in kcmil (thousands of circular mils) for very large cables.