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DC Wire Size Calculator
Estimate the minimum wire gauge and maximum fuse size for a 12V, 24V, or 48V DC circuit aboard your boat, based on ampacity and voltage drop.
Before you use this: this calculator gives a general estimate based on ABYC's wire-sizing methodology. It is not a substitute for a professional determination by a qualified marine electrician, and it does not replace a full ABYC-compliant installation review. Real-world factors, unusual ambient heat, non-standard insulation, aluminum or non-copper conductors, or derating this tool doesn't account for, can require a larger conductor than what's recommended here. When in doubt, size up, and verify anything safety-critical with a professional before wiring the circuit.
This tool covers DC circuits only. It does not calculate AC circuits, engine cranking/starting circuits, or lithium battery main feeders, and it does not determine where overcurrent protection must be physically located aboard the boat. Those require additional ABYC provisions beyond this calculator's scope. We are not liable for outcomes from installations based on this tool's output, see our Terms for the full disclaimer.
Your Report
| Circuit | Wire Gauge | Max Fuse | Watts | Notes |
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How This Is Calculated
Every wire size here is the larger (heavier gauge) of two independent checks: how much current the conductor can safely carry given its insulation rating, bundling, and installation location, and how much voltage it will lose over the length of the run. On short, high-current circuits, ampacity is usually the binding constraint. On long, lower-current runs, like navigation lights at the bow on a long boat, voltage drop usually wins. We show you which one applied to your circuit and why.
The wire-sizing methodology follows ABYC's structure, insulation temperature rating, conductor bundling, installation location, and a voltage-drop ceiling appropriate to the circuit (3% for circuits like main feeders, bilge pumps, navigation lights, and electronics, 10% for general lighting and accessories). The numbers behind this calculator are independently derived engineering estimates and are not guaranteed to be a reproduction of ABYC's guidelines. Always double check and verify calculations used by this table and if unsure, consult us or another qualified marine electrician.
Curious about the equipment on the other end of that wire? See our guides on inverter safety and selection and galvanic corrosion.
Want this professionally verified and installed?
We size, install, and certify DC and AC electrical systems to ABYC standards throughout San Diego County.
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