How Much Paint for a 20x20 Room?
Paint needed
3.75 gallons
A 20 by 20 room with nine foot walls, two doors, four windows, two coats.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Room perimeter, add all walls80 ft
- Wall height9 ft
- Doors2
- Windows4
- Coats2
- Coverage per gallon350 sq ft
Paint needed3.75 gallons
| Gross wall area | 720 sq ft |
|---|---|
| Less doors and windows | -102 sq ft |
| Net wall area | 618 sq ft |
| Area over 2 coats | 1,236 sq ft |
| Gallons, exact | 3.53 |
| Buy | 4 gallonsor 1 five gallon pail |
The material list this produces
| Paint, gallons | 4 |
|---|---|
| Primer, gallons (if bare or color change) | 2 |
| Painter's tape, rolls | 2 |
Coats compared
Coats is the input people get wrong, usually by hoping. Same room, one coat to three.
| Coats | Paint needed |
|---|---|
| 1 coat | 2 gallons |
| 2 coats | 3.75 gallons |
| 3 coats | 5.5 gallons |
What else matters here
Eighty feet of perimeter at nine feet is 720 square feet gross and 618 net. Two coats is 1,236 square feet, just under four gallons, which is the point where the five gallon pail is clearly the right buy rather than a close call.
A pail also solves the logistics. Four separate gallons means opening, stirring and pouring four times, and a room this size takes long enough that a can opened at the start behaves differently from one opened at the end. One batch, one consistency.
A room 20 feet across is big enough that lighting changes across it. Cut in and roll one full wall at a time rather than cutting the whole room and then rolling it, because a cut line that has dried before the roller reaches it will show as a picture frame around the wall.
What this calculator assumes
- A door is taken as 21 sq ft and a window as 15 sq ft. Deducting them matters on a small room and barely moves a big one.
- 350 sq ft per gallon is the usual figure on a smooth primed wall. Bare drywall, textured walls and deep color changes all drink more, so drop it to 300 if any of those apply.
- Ceilings and trim are not included. Run the ceiling as its own area.
Questions people ask
How much paint for a 20x20 room?
About 3.75 gallons for two coats on nine foot walls. Buy the five gallon pail rather than four gallons.
Is a 5 gallon pail cheaper than 5 gallons?
Almost always, and it is also one batch, so there is no shade variation between cans. The downside is handling: a full pail is around 50 pounds.
How much paint for a 20x20 garage?
The same wall figure applies, but bare block or unfinished drywall drinks far more. Drop the coverage figure above from 350 to 250 and prime first.
The paint calculator takes any dimensions you like and hands back the same list.