THE BASICS
1. Why prime at all
Primer is not extra paint: it is the layer that makes the topcoat work. On fresh drywall and joint compound it evens out absorption, so the finish doesn't look blotchy. Over stains — water marks, smoke, marker — it blocks the discoloration from bleeding through.
Repainting a similar color over a clean, sound wall? You can often skip primer. Going from dark to light, covering repairs, or painting new drywall? Prime first.
FIGURES
2. Primer coverage per gallon
Our practical reference for a multi-purpose primer is 350 sq ft per gallon per coat, based on KILZ 2's data sheet. Manufacturer sheets are measured on smooth, sealed surfaces; real walls absorb more, so treat the figure as a planning number.
| Container | Approx. coverage | Good for |
|---|---|---|
| Quart | ≈ 88 sq ft | Small patches and repairs |
| Gallon | ≈ 350 sq ft | One coat on a 12×12 room |
| 5-gallon pail | ≈ 1,750 sq ft | Two coats on ~900 sq ft |
KILZ 2 declares up to 400 sq ft/gal on ideal surfaces; 350 is the practical reference for real walls.
CRITERIA
3. How many coats of primer
One coat is enough for repainting over a sound surface or sealing minor repairs. Two coats are the safe call for fresh drywall — the first coat lifts the nap of the compound — and for blocking strong stains with a stain-blocking primer.
Plan topcoat numbers separately: primer gallons do not count toward the finish paint.
SHOPPING
4. How much to buy for your project
Take your wall area in square feet, divide by 350 per coat, and round up to the container you will actually buy. A 12×12 room with 8 ft walls is about 384 sq ft minus openings: roughly 1 gallon for one primer coat.
Ready to skip the math?
Open the paint calculator