How Much Paint Primer Do I Need?
Divide your wall area in square feet by 200 — the standard coverage for one coat of primer on drywall — and round up to a whole gallon. That covers one coat on one surface type; for a room with doors and windows to subtract, more than one coat, or a mix of surface conditions, the primer calculator does the same math with those factored in. This page is a quick reference table by wall area, plus a worked example for a job spanning several rooms with different primer needs.
Gallons needed by wall area
These figures assume one coat at the standard 200 sq ft/gallon rate and round up to the next whole gallon, since primer is sold in whole cans. Find the row closest to your total wall area (perimeter × height, minus doors and windows).
| Wall area | Primer needed (1 coat) |
|---|---|
| 100 sq ft | 1 gallon(s) |
| 200 sq ft | 1 gallon(s) |
| 300 sq ft | 2 gallon(s) |
| 400 sq ft | 2 gallon(s) |
| 600 sq ft | 3 gallon(s) |
| 1,000 sq ft | 5 gallon(s) |
Primer coverage rate (200 sq ft/gallon): This Old House, citing Lowe's — the 200 sq ft/gallon figure sits at the conservative end of the commonly cited 200–300 range, on the reasoning that a little extra primer left over costs less than a mid-coat run to the store. Bare drywall or new construction typically needs exactly one coat; a heavily stained, glossy, or masonry surface can need a second coat or a different primer type entirely — see the calculator's FAQ for which situations call for which.
A full example: priming an apartment with two different primer types
A common real job mixes surface conditions across rooms, which means mixing primer types, not just totaling up gallons. Take a two-room repaint: a 240 sq ft hallway of new, bare drywall, and a 180 sq ft kitchen with visible grease residue and smoke discoloration near the stove. The hallway needs one coat of ordinary water-based primer: 240 ÷ 200= 1.2, rounded up to 2 gallons. The kitchen's grease and smoke mean a standard primer won't reliably block it, so it needs a shellac- or oil-based stain-blocking primer at two coats: 180 sq ft × 2 coats = 360 sq ft of coverage, and 360 ÷ 200 = 1.8, rounded up to 2 gallons of the stain-blocking product. The shopping list is two separate cans of two different primers — 2 gallons of water-based for the hallway, 2 gallons of oil- or shellac-based stain-blocker for the kitchen — not four gallons of one product, which is the detail a single combined area calculation would miss.