DC Wire Size Calculator

Enter your current (amps), circuit length, system voltage, and acceptable voltage drop (%) to find the correct DC wire gauge. The DC Wire Size Calculator returns the recommended AWG wire size, equivalent cross-sectional area (mm²), actual voltage drop, and a suggested fuse size — so your wiring is both safe and efficient.

A

The maximum continuous current the circuit will carry.

Nominal voltage of your DC system.

ft

Distance from power source to load (one way). Total wire length used will be doubled.

%

ABYC recommends ≤3% for critical circuits, ≤10% for non-critical.

Copper is standard for most DC wiring.

Bundled wires generate more heat; a derating factor is applied to ampacity.

Results

Recommended Wire Size (AWG)

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Cross-Sectional Area

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Actual Voltage Drop

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Actual Voltage Drop (%)

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Derated Ampacity

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Recommended Fuse Size

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Voltage Budget Breakdown

Results Table

Frequently Asked Questions

What wire size should I use for a 12V DC circuit?

It depends on the current and wire length. For a 12V system carrying 20A over 10 ft with a 3% voltage drop limit, 10 AWG copper wire is typically appropriate. Use this calculator with your specific values to get an exact recommendation, since longer runs or higher currents require larger wire gauges.

What size wire do I need for a 30A DC circuit?

For a 30A DC circuit at 12V with a 10 ft one-way run and 3% allowable voltage drop, 10 AWG copper is usually sufficient. Longer distances or lower voltage systems will require stepping up to 8 AWG or larger to keep voltage drop within safe limits.

Why does wire length matter for DC circuits?

In DC circuits, resistance accumulates over the entire length of the wire — both the outgoing and return conductors. Longer runs create more resistance, which increases voltage drop. This means the load at the end of the wire receives less voltage than intended, reducing performance and potentially causing damage.

What is an acceptable voltage drop for DC wiring?

ABYC (American Boat and Yacht Council) and most industry standards recommend a maximum voltage drop of 3% for critical circuits (navigation, safety equipment) and up to 10% for non-critical loads. Staying within these limits protects equipment and ensures efficient operation.

What is wire bundling derating and why does it matter?

When multiple wires are bundled together, they trap heat generated by current flow, reducing each wire's safe current-carrying capacity. Standards require applying a derating factor — for example, 4–6 bundled wires are typically derated to 70% of their rated ampacity. Ignoring this can cause insulation melting or fire.

What is the difference between AWG and mm² wire sizing?

AWG (American Wire Gauge) is the standard used in the US and Canada — lower AWG numbers mean thicker wire. mm² (square millimeters) measures the actual cross-sectional area of the conductor and is the standard used in Europe and Australia. The two systems are interchangeable with a conversion factor; for example, 10 AWG ≈ 5.26 mm².

Should I use copper or aluminum wire for DC circuits?

Copper is strongly preferred for most DC wiring due to its lower resistivity, better conductivity, and easier termination. Aluminum wire has higher resistance, meaning you need a larger gauge to carry the same current. Aluminum is sometimes used in large commercial or solar installations to reduce cost and weight.

How do I size a fuse for my DC circuit?

The fuse protects the wire, not the device. Select a fuse rated at or slightly above the circuit's maximum continuous current, but never exceeding the wire's rated ampacity. For example, a 10 AWG copper wire rated at 30A should be protected by no more than a 30A fuse. Place the fuse as close to the positive terminal of the battery as possible.

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