About GutterMath
GutterMath exists because gutter sizing is rainfall arithmetic, and nobody shows the rain.
Gutters are sized by one multiplication — roof area times rainfall intensity — yet most replacements copy whatever size is already hanging, and undersized gutters overflow in exactly the storms they exist for.
The calculators run the standard method: 5-minute rainfall intensity from NOAA data, K-style vs half-round capacity, downspout counts by flow, and the quarter-inch-per-ten-feet slope rule. Every input is editable and every output shows its formula.
We are educators, not installers. Nothing here sells gutters, and your roof measurements never leave your browser.
What makes GutterMath different
- Your numbers never leave your browser. Every calculator on GutterMath runs entirely on your device. We never see, store, or transmit the figures you enter — there are no accounts and no server-side processing of your inputs.
- Published methodology. Each calculator page explains the exact formula it uses and the assumptions behind it, so you can check our work or reproduce it in a spreadsheet.
- Free, forever, without a paywall. GutterMath is supported by advertising. There is no premium tier, no email gate, and no upsell.
Independence
GutterMath is an independent educational project. We are not affiliated with, endorsed by, or acting on behalf of any government agency, lender, insurer, or the organizations whose formulas and public data we reference (such as SMACNA and NOAA rainfall-atlas methods). All trademarks and referenced standards belong to their respective owners.
Questions, corrections, or suggestions are genuinely welcome — get in touch.