Paint Primer Coverage Calculator
Calculate how much primer you need before painting walls or ceilings, based on surface area, number of coats, and primer spread rate.
Why Use Primer?
Primer seals porous surfaces, improves paint adhesion, and helps achieve true paint color in fewer coats. Using primer reduces the number of paint coats needed — saving time and money overall.
Calculating How Much Primer You Need
The key number is the spread rate — how many square feet one gallon of primer covers. Most standard primers cover 250–400 sq ft per gallon on smooth drywall. Porous surfaces (bare wood, new drywall, masonry) absorb more primer — use a lower spread rate.
The Formula Exact gallons = (surface area × number of coats) / spread rate With waste factor: gallons needed = exact gallons × (1 + waste % / 100) Gallons to buy = round up to the nearest whole gallon
Waste Factor 10% waste factor is standard for professional painting. Add 15–20% for complex rooms with lots of corners, edges, or cut-ins.
One Coat vs Two Coats For new drywall or a drastic color change, two coats of primer are recommended. For repaints on smooth previously-painted walls, one coat is usually sufficient.
Quarts vs Gallons If you need less than 1 gallon, buying a quart (quarter gallon) is more cost-effective. This calculator shows both options to help you decide.