Primer Calculator
Estimate gallons of primer for a surface.
Enter the area you're priming, subtract doors and windows, and set the primer's coverage to get the gallons needed. Primer usually goes on in one coat and covers a bit less area per gallon than finish paint.
How it works
Primer needed = (area − openings) × coats ÷ coverage. Primer typically covers about 200–300 square feet per gallon — less than topcoat because it soaks into porous and patched surfaces. One coat is normal; bare or stained surfaces may need two.
Frequently asked questions
How much primer do I need?
Subtract openings from the wall area, multiply by coats, then divide by the coverage (about 300 sq ft per gallon). A 400 sq ft room with 40 sq ft of openings needs a little over 1 gallon for one coat.
Does primer cover less than paint?
Yes — primer soaks into porous and patched surfaces, so it often covers only 200–300 sq ft per gallon versus 350–400 for finish paint.
Do I need two coats of primer?
Usually one is enough, but bare drywall, raw wood, stains, or a big color change can call for a second coat.
Is this calculator free and private?
Yes. Every CubicCabin calculator runs entirely in your browser, so the numbers you enter are never uploaded or stored. There's no sign-up, no limits, and it keeps working even if you lose connection after the page loads.