How to calculate paint
Gallons = (Wall area × Coats) ÷ 350
Worked example. Paint you'll need: 2.25 gallons.
Example inputs — Room length: 14 ft; Room width: 12 ft; Wall height: 8 ft; Coats: 2 coats; Doors & windows: 3. Starting values are illustrative.
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
One gallon covers about 350 square feet. We subtract roughly 18 sq ft per door or window.
Assumptions & limitations
- Material estimates only — buy 5–10% extra for waste and cuts.
- Check coverage figures on your product label.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
Do I need primer?
Use primer on new drywall, stains, or when making a big color change.