About CoatMath
CoatMath is an independent project owned and run by Matt, a person, not a company or news organization. It is a free, no-signup tool site: Know exactly which cans to buy.
Purpose
I built CoatMath to help people work out how much paint and primer to buy for a room, ceiling or house exterior, and which cans make the cheapest shopping list with real numbers instead of guesses. The calculators run in your browser, show their formulas, and let you change every assumption. The guides explain the numbers behind the tools in plain language.
Data sources
Paint needs follow standard geometry (wall area = perimeter × height, minus doors and windows; gallons = area × coats ÷ coverage). Coverage ranges of 300 to 400 sq ft per gallon, 350 as a rough default, and notes on textures, sheen and primer come from PaintCare's Buy Right guide (paintcare.org/buy-right). Default prices are typical 2026 US figures that you can edit.
How we keep it accurate
The math is covered by automated tests with hand-computed answers, figures show their source and update date where possible, and the site was last updated October 17, 2026. If you spot an error, please tell me and I will fix it.
Disclaimers
Estimates only. Check your paint can’s label for coverage. CoatMath is currently at matt5516.github.io/paint-calc; coatmath.com is the planned domain, pending the owner’s approval. Not affiliated with any paint brand or store. See the terms of use and privacy policy.
Contact and feedback
Email matt63sorensen@yahoo.com, use the Feedback button on any page, or open an issue on GitHub. More on the contact page.