Tired of buying too much paint or running out mid-project? RoomPaintCalc is a free calculator that tells you exactly how many gallons you need — no sign-up, no apps. Enter room dimensions, add doors/windows (auto-subtracted), set coats and coverage, get your answer instantly. Most calculators ignore doors/windows or hide behind a sign-up wall. RoomPaintCalc is one clean page. Supports imperial & metric.