Free online tool
DC Cable Size Calculator
Built for 12V, 24V and 48V systems: solar arrays, batteries, inverters and DC-DC runs, where low system voltage makes voltage drop the deciding factor far more often than ampacity alone.
Recommended conductor size
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Fit a fuse or breaker close to the battery, sized to protect the cable. This estimate is for planning only. Confirm against your equipment manufacturer's guidance and local code.
Why DC and low-voltage wiring is different
Power is volts × amps, so at 12V a load draws roughly 19 times more current than the same wattage would at 230V. Cable size is driven mostly by current, which is why a modest 1-2 kW load on a 12V battery bank needs surprisingly thick cable. It's also why voltage drop, not ampacity, is usually what forces the size up on solar, battery and inverter runs. Keeping runs short and using a tighter voltage-drop limit (2-3% rather than 3-5%) protects both efficiency and the usable capacity of your battery.
Frequently asked questions
Why does a 12V system need thicker cable than 230V for the same power?
Power equals volts times amps, so at a lower voltage the same wattage means much higher current. A 1000W load draws about 4.3A at 230V but around 83A at 12V. Since cable size is driven mainly by current, low-voltage systems need thicker conductors for the same delivered power.
What voltage drop limit should I use for solar and battery wiring?
Many solar and marine wiring guides recommend 2–3% on any single run, sometimes tighter (1–2%) for panel-to-controller runs, to avoid losing usable power.
Do I need a fuse close to the battery?
Yes. A fuse or breaker sized to protect the cable should sit as close as practical to the battery terminal, since a short near the battery can push very high fault current through an unprotected cable.