How much primer you need
One coat over everything you will paint, over what a gallon of primer covers. Sherwin-Williams gives primer 200 to 300 square feet a gallon; the page works at 250, the middle. A 12 by 12 foot room with 8 foot walls, one door and one window, is 349 square feet of wall: 349 over 250 is 1.40 gallons, so two gallon cans of primer. The two coats of paint over it are worked out beside it, 1.99 gallons, and both go on the same shopping list.
Lowe's calculator works primer at 200 square feet a gallon. For its own example, a 12 by 10 foot room with a door and a window, it prints 1.6 gallons of primer — and 0.9 gallons of paint, because it counts one coat. Type Lowe's own figures under Assumptions — 200 for the primer and 16.66 square feet for the door — and the page gives the same 1.6 gallons of primer, and 1.83 gallons for the two coats of paint.
When you need primer
Inch Calculator lists three cases:
- new drywall;
- a change between a light color and a dark one;
- stains to cover.
Without primer, Inch advises two or three coats of paint when the color changes a lot; the page says so when it is set to one coat with no primer. Switch "Primer" to none and the primer comes off the list; the paint stays.
What primer covers
Everything the page paints: the walls, the ceiling if you include it, and the trim. On the walls and ceiling of the same room, 493 square feet, it is 1.97 gallons — still two cans. A coat of primer is one coat; the coats you choose are for the paint over it.
| Primer covers | 12 × 12 walls | Walls and ceiling |
|---|---|---|
| 200 ft²/gal | 1.75 gal | 2.47 gal |
| 250 ft²/gal | 1.40 gal | 1.97 gal |
| 300 ft²/gal | 1.16 gal | 1.64 gal |
Buying it
Primer comes in the same quarts, gallons and 5-gallon pails as paint, and the page picks the cheapest mix of them, the prices beside the primer's row of the shopping list. Those prices are our own estimates, not a store's: type yours. We are not connected with any brand or store named here.