Solar Calculators
Every tool on the site, in the order you need them. All are free, none need a signup, and every one shows the arithmetic behind its answer.
Start here
Full system calculator
What does my whole build need?
Start here. Sizes panels, battery, controller, inverter, cable and fuses together, and estimates cost.
Step 1
Battery size calculator
How many amp-hours do I need?
You know your appliances and want the bank size, with LiFePO4 and AGM compared.
Step 2
MPPT charge controller calculator
What size controller for my array?
You have picked panels and need the controller amperage, with cold-weather margin applied.
Step 3
Inverter size calculator
What size inverter, and what fuse?
You run AC appliances and need continuous watts, DC current draw and the battery-cable fuse.
Step 4
Wire size & voltage drop calculator
What gauge cable, and what fuse?
You know the load and the run length. Checks ABYC ampacity and a 3% voltage-drop limit.
Which one do I actually need?
If you are planning a build from scratch, use the full system calculator and ignore the rest. It sizes everything together, which matters because the parts are linked: the battery follows your daily load, the controller follows the array, and the cable follows the inverter. Changing one changes the others.
The single-purpose tools are for when you already have most of a system and need one number. Replacing an inverter and want to know if your existing cable still passes? Use the wire calculator. Adding two panels and wondering whether the controller copes? Use the MPPT calculator.
The standards behind the numbers
Every tool uses the same engineering basis, documented on the about page: ABYC E-11 105 °C ampacity for cable, a 3% voltage-drop limit measured over the round-trip run, a 0.75 real-world solar derate, 0.8 depth of discharge for LiFePO4 and 0.5 for AGM, and a 1.25 margin on controller and inverter sizing. Nothing is hidden, and no result steers you toward a particular brand.
Prefer a table to a tool? The sizing chart lists worked figures by usage profile, van type and region, all generated from these same formulas. You are also welcome to put the calculator on your own site free of charge.