Solar Calculators
Solar panel sizing, wire gauge, and battery bank calculators for off-grid and grid-tied systems.
Three calculators for planning a solar system: how many panels you need and what they'll save, how big a battery bank should be, and what size cable each run needs. The panel calculator covers every US state and UK region, and anywhere else from your peak sun hours.
3 tools available · Free · No signup required
All 3 tools
Which tool to pick
- Solar Panel Calculator: the first step for a grid-tied home: size the system from your electricity bill or an appliance list, with the cost, incentives and payback time.
- Solar Battery Bank Calculator: off-grid or backup power: the bank for your daily use and days of autonomy, how long it runs essentials in a power cut, and whether your panels can recharge it.
- Solar Wire Size Calculator: choosing cable for each run, from the panels, between inverter and battery, and on load circuits, so voltage drop stays within limits.
Plan the system in this order
Begin with how much electricity you use. A year of bills gives the most honest figure; an appliance list works if you're building off grid. That one number drives the panel count, the battery size and, through the currents involved, the cable.
Size the panels next, then the battery if you want one, and leave wiring until last, because cable size depends on the current each run carries and how long it is. When the battery calculator asks for your array size, use the figure from the panel calculator so the two agree. Keep the results together: an installer will ask for the same numbers, and having them makes quotes easier to compare.
Guides
How Many kWh Solar Battery Do You Need for Your Home?
Work out how many kWh of solar battery your home needs: size for essentials first, avoid the nominal-capacity trap, and check it with a free calculator.
Is Solar Worth It? Payback by US State and UK Region
How long solar panels take to pay for themselves in all 50 US states, DC and 7 UK regions, from 2026 electricity prices, installed costs and modelled sunshine.
Solar Panel Sizing: How Many Panels Do You Need?
A complete guide to calculating the right solar panel capacity for your home or off-grid system based on your energy consumption.
About Our Free Solar & Energy Calculators
Size a solar array against your actual consumption, work out the battery bank capacity you need for your target days of autonomy, and check wire gauge against current and run length for both off-grid and grid-tied systems.
All calculations run in your browser with no server calls, so your consumption figures and system details stay on your device.
These calculators give you a well-founded starting point, but a real installation depends on your latitude, roof orientation and shading, local irradiance data, and the electrical code where you live. Have any system you intend to build reviewed and signed off by a qualified installer — undersized conductors in particular are a fire risk.