L-01 · Free tool
Boat wire size and voltage drop
The cable cross-section for a 12 or 24 V load, from the current, the one-way run and the drop you can accept.
Inputs
System voltage
Allowed voltage drop
ResultValid for 12 and 24 V DC circuits with copper cable, 1–200 A and 1–30 m one way. Voltage drop only. Check the cable's current rating, insulation temperature and your class rules too.
Minimum cross-section25 mm²calculated 23.8 mm² · next standard size up
Voltage drop with this size0.34 V · 2.9 %
US gauge2 AWG · 0.26 V · 2.1 %
Required area47,025 cmil
Round-trip length12 m · 39.4 ft
Allowed drop0.36 V of 12 V
Copper constant0.0179 Ω·mm²/m (K 10.75)
Method
How it is calculated.
The standard voltage-drop formula for DC boat circuits, with the copper constant from ABYC E-11. The result is rounded up to the next standard metric size and the next AWG gauge.
A = ρ · 2L · I / ΔV
CM = K · I · L / E (the same formula in US units: circular mils, feet)
Across-section, mm²
ρcopper, 0.0179 Ω·mm²/m (K = 10.75 Ω·cmil/ft in ABYC E-11; slightly above pure copper at 20 °C, 0.0172)
2Lround-trip length, positive and negative
Icurrent, A
ΔVallowed drop, V: 3 % for critical loads (panel feeders, navigation lights, electronics, bilge blowers), 10 % for non-critical ones such as cabin lighting
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