Free solar calculators that respect your privacy
SolarSize is a collection of free online solar calculators — panel sizing, system cost, savings, payback, ROI, battery sizing and output — that run entirely in your browser with no sign-up, no account, and no tracking of what you type into them. Every calculator on this site works the moment the page loads, and the numbers you enter never leave your device.
The site started from a simple frustration: most “free” calculator websites are slow, covered in pop-ups, and quietly harvest the data you paste into them. We built SolarSize to be the opposite — fast, clean, and private by design. If a calculator can run in your browser, it does; there is no server-side processing of your inputs and nothing to leak in a breach.
Who SolarSize is for
Homeowners thinking about solar panels for the first time. People comparing quotes who want to check the numbers themselves. Homeowners in the US, UK and Pakistan who want sizing and costs in their own currency and sun conditions. Anyone who needs to know how many panels they need, what it will cost, and how long payback might take — without creating yet another account.
Our calculators are built for real-world use, not demos. The solar panel calculator uses the standard sizing formula (daily kWh ÷ peak sun hours ÷ a 0.8 system derate) and allows about 18 sq ft of roof per panel. The battery calculator accounts for depth of discharge and inverter losses. Savings are always shown as ranges with their assumptions visible — never as single-number promises. When a calculator has a standard or best practice behind it, we follow it — and we say so in the methodology notes on each page.
Our editorial standards
Every calculator page includes three things: a plain-language explanation of what the calculator does and the method behind it, step-by-step usage instructions, and answers to the questions people actually ask about the topic. The “direct answer first” format means you get the key fact in the first paragraph, with deeper detail below for those who want it.
We document our sources and formulas on each calculator page so you can verify the math yourself. Content is reviewed and updated at least once a year, or sooner when standards, formulas, or best practices change. If we find an error, we fix it and note the correction — accuracy matters more than looking polished.
We do not publish AI-generated filler. Each page is written to genuinely answer its topic, because thin content helps nobody and search engines increasingly agree.
What we don’t do
- No data collection on calculator inputs. What you type into a calculator stays in your browser. We cannot see it, sell it, or lose it.
- No accounts, no sign-ups, no paywalls. Every calculator is free and complete. There is no “pro” tier gating the useful features.
- No dark patterns. No fake download buttons, no countdown timers, no misleading ads disguised as calculators.
- No professional advice. Our calculators are estimating aids. They do not replace a qualified solar installer, a licensed electrician, or local regulations — see our Disclaimer.
How the site stays free
SolarSize is currently free to run and use, with no advertising on the site. In future, display advertising may help keep every calculator free without charging you or selling your data — and because our calculators run client-side, advertisers would never see what you type into them either. If you prefer, an ad blocker won’t break anything; the calculators work exactly the same.
Get in touch
Found a bug, have a calculator request, or spotted an error in our content? We genuinely want to hear about it — reader corrections have improved several calculators already. Head to our contact page to reach us. We read everything and respond to most messages within a few business days.