Calculate primer gallons from wall or ceiling square footage, number of coats, product coverage and waste allowance before painting new or repaired surfaces.
Enter your measurements and material details.
Fresh drywall, patched areas and porous masonry may absorb primer differently.
The calculator uses the surface area you already measured, multiplies it by the number of primer coats and divides by the coverage stated for one gallon. A user-controlled allowance is then added.
Use net paintable surface area. If the project includes walls and ceiling, add those areas before entering the total. Product coverage should come from the actual primer label because high-build, stain-blocking and masonry primers can differ.
At 350 square feet per gallon, roughly three gallons are needed for one coat before allowance.
Many jobs use one coat, while stains, porous surfaces or major color changes can require more.
Not necessarily. Use the coverage printed on the primer you plan to buy.
Yes if you enter the exterior surface area and the correct product coverage.
Yes when the calculated amount falls between container sizes needed to finish the coat.
Using the example inputs shown in the calculator — Surface area (sq ft) = 500, Primer coats = 1, Coverage per gallon (sq ft) = 350, Extra allowance (%) = 5 — the result is 1.5 gallons. This demonstrates the formula with a complete set of numbers rather than a hidden assumption.
The result breakdown also shows Surface with coats: 500 sq ft; Rounded purchase: 2 gal. Replace the example values with field measurements and the exact product coverage, yield or package size you plan to buy.
For this primer calculator, the inputs with the greatest practical effect are surface area, primer coats and coverage per gallon. Recalculate when any of those change; do not reuse a result from a different room, run, layer depth or product specification.
Primer Calculator is intended to help with quantity planning and arithmetic. It does not inspect the site, choose structural dimensions, determine code compliance or replace manufacturer installation instructions. Conditions such as slope, substrate quality, moisture, soil, framing, access and workmanship can change the final amount required.
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