12V Wire Gauge Calculator

12V DC Wire Size Guide

Low-voltage DC circuits are sensitive to voltage drop. Automotive, solar, and RV wiring should stay near 3% drop so lights stay bright and motors start reliably. This calculator finds the smallest AWG that meets both ampacity and drop limits.

DC Voltage Drop Formula

$$V_{\text{drop}} = 2 \times I \times R \times L$$

The factor of 2 accounts for the outbound and return conductors. $I$ is load current in amperes, $R$ is wire resistance in ohms per 1000 ft, and $L$ is one-way length expressed in thousands of feet.

Percent drop:

$$\%\text{drop} = \frac{V_{\text{drop}}}{V_{\text{source}}} \times 100$$

Example: 10 A over 20 ft on 12 V with 8 AWG copper gives about 2.5% drop. Related: 24V Wire Size Calculator and Voltage Drop Calculator.

Frequently Asked Questions

What wire for 12V at 10 amps?

Short runs may use 14 AWG, but 20 ft or more often needs 10 AWG or 8 AWG copper to stay under 3% drop. Enter your exact length and current for a precise answer.

Why is 3% the default max drop?

12 V systems have little headroom. A 3% drop on 12 V is only 0.36 V. Many installers target 3% for critical loads and 5% for non-critical circuits.

Does aluminum work on 12V DC?

Yes, but aluminum has higher resistance. You will need a larger gauge than copper for the same current and length. Use proper terminations to avoid corrosion.

One-way or round-trip distance?

Enter one-way length only. The formula already doubles the path with the factor of 2.

What about fuse or breaker size?

Protect the wire with a fuse or breaker rated at or below the conductor ampacity. This tool sizes the wire; overcurrent protection is a separate step.

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12V Wire Size Calculator

12V DC Wire Size Guide

DC Voltage Drop Formula

Frequently Asked Questions

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