How Much Paint for a Garage?
The short answer: 4 gallons for a 20x20 garage. But the walls and the floor are two completely different jobs.
A 20x20 garage with 8-foot walls needs 4 gallons of paint for two coats. That assumes you subtract the garage door and a pedestrian door. If your garage walls are bare concrete block rather than drywall, expect to use 25 to 40 % more paint, because masonry absorbs heavily.
Estimates only. Textured walls, high ceilings, sprayers and major colour changes can all increase the amount you need. Always buy slightly more than the calculation suggests.
Paint needed by garage size
| Room / surface | Surface | Coats | Paint | Paint cost |
|---|---|---|---|---|
| Single garage, 12x20, drywall | 407 sq ft | 2 | 3 gal | $105 |
| Single garage, 12x20, bare block | 407 sq ft | 2 | 4 gal | $140 |
| Double garage, 20x20, drywall | 535 sq ft | 2 | 4 gal | $140 |
| Double garage, 20x20, bare block | 535 sq ft | 2 | 5 gal | $175 |
| Double garage with ceiling, 20x20 | 935 sq ft | 2 | 6 gal | $210 |
Two coats. The door count is raised to 5 because a standard garage door is about 80 sq ft, roughly four times a normal door.
The garage door is the whole game
A standard single garage door is 8 to 9 feet wide and 7 feet high — about 60 to 80 square feet. That is four times the allowance for an interior door.
This is why the calculator above is set to 5 doors for a garage: it counts the garage door as four normal doors plus one pedestrian door. If you leave it at the default of one, you will overbuy by roughly a gallon.
Measure your garage door and divide by 21 to get the right count. A 16-foot double door at 7 feet high is 112 square feet — that is 5.3 normal doors on its own.
Bare masonry changes everything
If your garage walls are unpainted concrete block or brick, the coverage figures on the paint can do not apply. Porous masonry absorbs paint the way a sponge absorbs water.
- Previously painted block: use 300 sq ft per gallon.
- Bare block, first coat: use 250 sq ft per gallon, or even less.
- Bare block, second coat: absorbs much less, so the average works out closer to 300.
A block filler or masonry primer before topcoat is not optional on bare block. It seals the surface and typically saves you a full coat of expensive topcoat.
The garage floor is a completely different product
Do not use wall paint on a garage floor. It will peel within months under tyre traffic and hot rubber.
Garage floors need a two-part epoxy coating, or a dedicated concrete floor paint. Epoxy is measured differently: a typical garage epoxy kit covers 250 to 500 square feet, so a 20x20 floor at 400 square feet needs one large kit, plus a separate primer if the concrete is bare or has been etched.
The critical step is surface preparation, not the product. Concrete must be etched or ground and completely dry before epoxy. Epoxy applied to smooth, sealed or damp concrete fails — this is the most common reason garage floor coatings peel.
Frequently asked questions
How much paint for a 20x20 garage?
4 gallons for two coats on the walls, assuming drywall and a typical garage door. Bare concrete block pushes that towards 5 or 6 gallons.
What kind of paint do you use on garage walls?
A durable acrylic or latex in satin or semi-gloss. Semi-gloss is easier to wipe down, which matters in a garage, but it shows wall imperfections more.
Can I use wall paint on a garage floor?
No. Tyre traffic and hot rubber will peel it. Use a two-part epoxy coating or a dedicated concrete floor paint instead.
Do I need to prime concrete block before painting?
Yes. Bare block is highly absorbent and a masonry primer or block filler will save you a coat of topcoat and give a far more even finish.