Wire Size Calculator

About the Wire Size Calculator

Recommends a minimum copper wire size (AWG / mm²) for a given load current, based on typical ampacity ratings. Always confirm against your local electrical code.

How to use this calculator

1. Enter the current in amperes, using the value your circuit will actually draw.
2. Choose the wire material and any other settings the calculator asks for, such as copper or aluminum.
3. Review the recommended minimum wire gauge, then compare it with your application requirements.
4. If the wire run is long or the load is continuous, choose a larger wire size when needed.

The formula explained

This calculator estimates the minimum wire gauge needed for a given current by comparing the load to standard ampacity limits. It then recommends a wire size that can safely carry at least that current under the selected conditions.

• I = current in amperes
• A = wire cross-sectional area
• AWG = American Wire Gauge size
• L = wire length

Step by step method

1. Find the current your circuit will draw, in amperes.
2. Use the calculator to match that current to a wire gauge with enough ampacity.
3. If the wire is long, increase the size to reduce voltage drop.
4. Check local electrical codes and device instructions before installing the wire.

Worked example

Problem. Find a minimum wire gauge for a device that draws \(15\) amperes on a copper circuit.

1. The load current is \(I = 15\) amperes.
2. A common minimum choice for a \(15\)-amp copper circuit is \(14\) AWG, but a larger wire such as \(12\) AWG is often chosen if the run is long or the load is continuous.
3. So the calculator would recommend at least \(14\) AWG, with \(12\) AWG as a safer upgrade in many cases.

Tips and common mistakes

• Do not assume every wire size works for every material, because copper and aluminum have different ampacity.
• For long runs, a wire that is technically large enough may still be too small because of voltage drop.

Frequently asked questions