Wire Gauge Ampacity Calculator

A wire has to be thick enough to carry its current without overheating, and short enough, or thick enough, that it does not drop too much voltage on the way. This checks an AWG wire both ways: the current it can safely carry as a single wire or in a bundle, and the voltage it loses over your run. It is built for low-voltage DC maker projects.

Two different limits

Picking a wire gauge is really answering two questions. First, can the wire carry the current without getting hot, which is ampacity. Second, will too much voltage be lost over the length of the run, which is voltage drop. A wire can pass the heat test and still fail the drop test on a long run, or the reverse on a short fat cable. This page shows both so you size for whichever is tighter.

Open air versus bundled

The same wire carries more current in open air than it does crammed into a loom or a conduit, because a single wire sheds its heat and a bundle traps it. That is why there are two ampacity numbers here. Use the open-air figure only for a single wire with room to breathe. For anything run in a bundle, a sleeve or a conduit, or packed into an enclosure, size to the lower bundled number and leave headroom.

Why voltage drop matters

Every foot of wire has a little resistance, and current through resistance loses voltage, which the load never sees. On a long run to a motor or a light, a thin wire can drop enough that the motor is weak or the LEDs dim. The drop grows with current and length and shrinks with thicker wire. A common target is to keep it under three percent for sensitive electronics, and under five to ten percent for motors and lighting.

This is for low-voltage DC, not your house

These figures suit the wiring makers actually do: robots, LED strips, battery packs, twelve and twenty-four volt automotive and solar. House and mains wiring is a different world, governed by electrical code, tied to insulation type, conduit fill and breaker size, and it is work for a licensed electrician. Do not size a wall circuit from a hobby chart. For your low-voltage projects, though, this gives you a safe, honest starting point.

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