AWG Wire Resistance Chart, with Voltage Drop Distances

The second and third tables turn those resistances into something you can use on site: the longest one-way run for each size before the drop passes the usual branch-circuit limit. For your own voltage, load and distance, use the voltage drop calculator.

Resistance by wire size

Each step down in AWG number is a thicker wire with less resistance. Aluminum conducts less well than copper, so an aluminum wire has more resistance than a copper one of the same size.

How far each copper size can run

These distances hold the drop to 3 percent, the limit most wire sizing tables use for a branch circuit. Double the voltage and a size can run twice as far at the same current; double the current and it can run only half as far.

How far each aluminum size can run

Aluminum is common for large feeders and service conductors because it is lighter and cheaper, and it is sized up to make up for its higher resistance.

Using these figures

• The resistances are for the conductor temperature building wire is normally rated at. A cooler wire has slightly less resistance, so the figures err on the safe side for most runs.
• Voltage drop is one of two checks. The electrical code also sets the smallest wire for each breaker and load, and the larger of the two answers wins.
• On AC circuits these figures leave out the small effect of inductance, which matters mainly for very large conductors and long feeders.
• The common targets are 3 percent on a branch circuit, 2 percent on a feeder and 5 percent in total from the source to the farthest load.

Common questions

Using these figures

You are welcome to cite the tables on this page. Please link to this page as the source, and check the maker's current data sheet before you rely on a single figure.