PaintCalc exists because of a receipt. Two extra gallons of tinted paint, bought on the advice of a calculator that took room dimensions, ignored the doors and windows, claimed 400 square feet per gallon, and never once asked how many coats were planned. The cans couldn’t be returned — custom colors rarely can — and they’ve been decorating a garage ever since. Every paint calculator on the web did some version of that math, so this one does the other version.

The philosophy: buy the plan, not the volume

The site’s one job is answering “how much paint do I need” the way a paint-store counter would: net the openings out of the wall area, multiply by actual coats, divide by a coverage rate that matches reality rather than the label’s optimism, and round to what you can actually purchase — gallons and quarts, or 1 / 2.5 / 5 / 10 litre tins. Ceiling and trim get their own lines because they’re different cans sitting on different shelves. Every assumption — the ~20 sq ft door, the ~350 rate, the US gallon at 3.785 litres — is printed, editable, or both.

How the numbers are sourced

Coverage presets come from the range manufacturers actually print — ~350–400 sq ft/gal for US interior paint, ~10–12 m²/L for UK/EU emulsion — discounted toward the figure painters plan around. Door and window defaults are the standard deductions estimators use. Articles cite the same arithmetic the tool runs; where a number is a range or an opinion, it says so on the page instead of inside a black box.

What it deliberately isn’t

No room-painting visualizer, no brand matching, no account, no app. One calculator, six guides, and a pricing line for the cans — the tools page works offline after it loads, and the math runs entirely in your browser.

The neighborhood

PaintCalc sits on nxtolerance.com alongside sibling single-purpose tools like EVCharge (EV charging time and cost), PowerBill (what your appliances cost to run) and PaceCalc. Same deal everywhere: one job, honest arithmetic.

Corrections welcome

Coverage rates drift as formulas change, regional can sizes vary, and every trade has a convention this page might have missed. If a number here disagrees with the can in your hand, the contact page is the shortest path to a fix — corrections are the mail we most want.