Boat Wire Size Calculator
Calculate the minimum marine wire size needed to keep DC voltage drop within your selected limit. Enter the system voltage, current, one-way cable distance, and allowable voltage drop.
Understanding Marine Wire Sizing
Marine DC wire sizing is strongly affected by voltage drop because 12V and 24V systems operate at relatively low voltage. This calculator uses the circular-mil voltage-drop method with K = 10.75 for copper boat cable and doubles the entered one-way distance to account for the positive and negative conductors.
How the calculation works
The calculator then selects the smallest standard AWG conductor in its table whose circular-mil area is at least as large as the calculated requirement.
3% vs 10% voltage drop
A 3% target is used for critical circuits where voltage drop can affect safety or essential operation. A 10% limit is used for non-critical circuits in the ABYC-style method represented here. The applicable requirement depends on the circuit and installation.
Important: voltage drop is not the only sizing check
Round-trip distance matters
If the source-to-load distance is 20 ft, the voltage-drop calculation uses 40 ft of conductor because current travels out to the load and returns through the negative conductor.