Priming Plan
Primer covers less than paint. Buy for the primer's own rate, off its own tin, and decide first whether you need it at all.
BFCBrilliance · bfcbrilliance.com/tools/primer-calculator
The job
- Room
- Date
- Surface type
- Perimeter
- Height
- Deductions
- AREA
- Coverage from the TIN
- Coats
- GALLONS
- Product
Coverage, and the gap that catches people
- PAINT, typical
- 300-400 sq ft/gal — 350 is the working figure
- PRIMER, typical
- 200-300 sq ft/gal
- ⚠ So the same wall needs
- about 40% MORE primer than paint
- Bare / thirsty surfaces
- use the LOW end — 200
- ⚠ Your tin's figure
- beats every default, including this one
- Coats
- ONE, usually — primer is preparation
- Door
- about 21 sq ft
- Average window
- about 15 sq ft
Do you actually need it?
- New drywall, bare wood, plaster, masonry
- YES — not optional
- Big colour change, dark to light
- YES — use a TINTED primer
- Glossy or slick surface
- YES — adhesion, not absorption
- Stains, smoke, water marks, knots
- YES — STAIN-BLOCKING primer specifically
- Sound painted wall, similar colour
- usually not — wash it instead
- ⚠ Self-priming paint
- fine on sound painted walls; NOT on bare work
Before opening the tin
- Decided whether primer is actually needed for THIS surface
- Right TYPE chosen — stain-blocking if there is anything to block
- Tinted primer considered, if the colour change is large
- Coverage read off the tin, not assumed from the paint
- Bought for the PRIMER's rate — about 40% more than the paint
- Surface washed, filled, sanded and dust-free first
- Whole surface primed, not just the visible stain
- Expecting it to look patchy — the topcoat evens it out
- Recoat time on the tin checked before painting over it
Don't buy the same amount as the paint
Paint goes about 350 sq ft to the gallon; primer 200-300. At 250 that is 40% more primer for the same wall — so matching the paint quantity leaves you close to a third short. It is the single most common miscalculation on a priming job, and the calculator shows both numbers together so it cannot happen quietly.
Patchy after one coat is correct
Primer is a preparation layer, not a finish. It is meant to seal and even out absorption, not to look good. A second coat is unusual outside severe stain blocking or very porous masonry — and adding one because the wall looks uneven usually spends money solving a problem the topcoat would have solved.