About SolarSizr
Free, no-signup solar calculators for people who build their own systems.
SolarSizr is a small collection of free solar calculators for DIY and off-grid enthusiasts, the people wiring up a van, an RV, a boat, a cabin or a backyard shed. Every calculator runs entirely in your browser, needs no account, and is free to use.
Why SolarSizr exists
Sizing a solar setup is genuinely confusing when you start: what angle should the panels be at, how thick does the wire need to be, how big a charge controller do you need? Most large solar websites are built to sell you a rooftop installation, not to help you build your own system. SolarSizr fills that gap with clear, single-purpose tools that just give you the number you came for.
How the calculators work
The calculators use standard, published solar and electrical formulas, and we show the method openly on each page so you can check the reasoning:
- Solar panel angle — optimal tilt from your latitude and the sun's declination.
- Solar wire size — wire gauge from voltage drop and ampacity.
- Charge controller size — controller amps from array power and battery voltage.
Who is behind it
SolarSizr is built and maintained by an independent software developer with an interest in renewable energy and clean, useful web tools. It is an ongoing project, and new calculators are added over time.
A note on accuracy
The results are planning estimates based on standard formulas. They are a great starting point, but they do not replace local electrical code or the advice of a licensed electrician or installer. Always double-check critical wiring, fuse and breaker sizing before you build.
Questions or suggestions? See the contact page.