Marine electrical calculators
Tools for 12V and 24V boat electrical systems — from cable sizing to solar panel yield.
Voltage drop calculator
Check cable is adequate for a run. See drop in volts and percentage against the 3% limit.
Cable sizer
Find the minimum cable size for a given run length, current and acceptable voltage drop.
Fuse size calculator
Find the correct fuse rating and type for any marine cable size.
Battery capacity calculator
Add your loads, set depth of discharge, and find the minimum bank size in amp-hours.
Battery runtime calculator
How long will your battery last at a given load? Enter bank size and current draw.
Solar panel yield
Calculate daily and monthly energy yield from your solar array. Includes UK sun hour data.
Solar & battery sizing
Size your solar array and battery bank together against your daily energy needs.
Ah / Wh / kWh converter
Convert between amp-hours, watt-hours and kilowatt-hours at any voltage.
Shore power calculator
Check whether your appliances fit within your marina shore power supply.
Marine electrical basics
Most small boat systems run at 12V DC, larger vessels at 24V. BS EN ISO 13297 and ABYC E-11 recommend a maximum 3% voltage drop for critical circuits. Always use tinned copper cable in marine environments — standard automotive cable corrodes rapidly in salt air.
Fuse every circuit as close to the positive supply as possible — within 300 mm of the battery or distribution bus.