12V / DC Wire Size Calculator
Size low-voltage DC wiring (automotive, RV, marine, battery) for voltage drop and free-air ("chassis") ampacity, and get a suggested fuse. Voltage drop is the governing constraint at 12/24/48 V.
US building/premises wiring? Use the NEC Wire Size Calculator. Solar array? The Solar PV Wire Size Calculator.
Input Parameters
Continuous load current
12, 24, or 48 V typical
One-way distance (round-trip used)
3% critical · 10% non-critical
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Results
Enter parameters and click Calculate
Low-Voltage DC Wire Sizing
Voltage drop is the driver
At 12/24/48 V, a small absolute drop is a large percentage, so voltage drop — not ampacity — usually decides the wire size. The tool picks the smallest conductor that meets both the ampacity floor and your voltage-drop target.
Voltage-drop target
Common marine/automotive practice (ABYC E-11): 3% for critical circuits (bilge pumps, navigation, electronics, panel main feeders) and 10% for non-critical loads such as general lighting.
Ampacity (free-air / chassis)
The ampacity floor is the single-wire-in-free-air ("chassis wiring") rating by gauge, reduced by a bundling derate when multiple conductors are loomed together. It ensures the wire will not overheat even before voltage drop is considered.
Fusing
The suggested fuse is the smallest standard rating at or above the load and at or below the conductor's ampacity, so it protects the wire. Place it at the source (battery positive).
Data & status
Free-air ampacities are the classic AWG "chassis wiring" chart, cross-checked across two independent references. This tool is Experimental and unverified; verify independently before final design.
References
- SAE J1128 (low-voltage primary cable construction)
- ABYC E-11 (AC & DC electrical systems on boats) — voltage-drop conventions
- AWG chassis-wiring ampacity chart (free-air single conductor)