Paint calculators
Primer Calculator
Primer is the coat nobody wants to buy and everybody regrets skipping. On new drywall it is non-negotiable: raw drywall and joint compound absorb paint at different rates, and without primer you get a blotchy finish that no amount of topcoat fully fixes. On bare wood it seals tannins and grain so your finish coats sit evenly.
How much you need depends almost entirely on the surface. Porous new drywall drinks primer at about 300 square feet per gallon; a sealed, previously painted wall stretches the same gallon to about 350. Pick your surface type below — or enter room dimensions and let the calculator derive the wall area — and get primer gallons rounded up to the nearest quart.
- Wall area
- 400 sq ft
- Primer needed (1 coat)
- 1 gal + 2 qt1.50 gal at ~300 sq ft/gal (new / unpainted drywall)
How we calculate this (with your numbers)
Primer = 400 sq ft ÷ ~300 sq ft/gal = 1.33 gal → 1 gal + 2 qt (rounded up to the nearest quart)
KILZ PVA drywall primer TDS: 300–400 sq ft/gal; we use the conservative end for porous drywall.
How the math works
Worked example
New drywall in a 12 × 12 ft room, 8 ft ceilings, 1 door, 2 windows:
- Wall area = 2 × 8 × (12 + 12) − 20 − 30 = 334 sq ft
- Primer = 334 ÷ 300 = 1.11 gallons
- Rounded up: 1 gallon + 1 quart
Limitations
Frequently asked questions
About one gallon per 300 square feet. New drywall is porous, so primer coverage drops to the low end of the range — KILZ PVA drywall primer lists 300–400 sq ft per gallon on its technical data sheet, and we use 300 for raw drywall. A 12×12 room (about 350 sq ft of wall) needs roughly 1.25 gallons: buy 1 gallon plus 1 quart.
Usually not, if the existing paint is in good condition and you are staying near the same color. You do need it for drastic color changes (dark to light), glossy surfaces that need scuff-sanding first, patched areas, and any bare spots.
One coat is standard for primer — it is a sealer and bonding layer, not the finish. The exception is severe stains or dark colors bleeding through, where a second coat (or a dedicated stain-blocking primer) may be needed.
For repaints in similar colors, yes — those products work well. For new drywall, bare wood, or drastic color changes, a dedicated primer seals and bonds better than any combo product. The calculator above assumes dedicated primer.
PVA (polyvinyl acetate) primer is the standard sealer for new drywall — it is inexpensive, seals the porous paper and joint compound evenly, and gives topcoats a uniform surface. That is why this calculator defaults new drywall to PVA coverage rates.
Related calculators & guides
- Interior paint calculator — includes a primer estimate for new drywall
- Paint cost calculator — add primer gallons to your budget
- How many coats of paint do walls need — when primer + 2 is the answer