How to use the paint calculator
- Pick your units. Feet and gallons, or meters and liters.
- Measure the room. Enter the room length, width and wall height.
- Count doors and windows. We take off about 20 sq ft per door and 15 sq ft per window.
- Choose coats and coverage. Two coats is the norm. Check the coverage on your paint label, usually 350 to 400 sq ft per gallon.
- Add the extras. Tick the ceiling or a coat of primer if you need them, and add a price to see the cost.
- Read what to buy. See the gallons or liters, rounded up to cans you can find on the shelf.
How to calculate how much paint you need
Working out paint for a room takes four steps. The calculator above does them all instantly, but it helps to know the math so you can sanity check the result at the store.
- Find the wall area. Add the length and width of the room, double it to get the perimeter, then multiply by the wall height. A 12 by 14 foot room with 8 foot walls has 416 square feet of wall.
- Subtract doors and windows. Allow about 20 square feet for a standard door and 15 square feet for an average window. In meters, allow about 1.9 and 1.4 square meters.
- Multiply by the number of coats. Two coats is the norm for an even finish, so double the paintable area.
- Divide by the coverage. A gallon of interior paint covers around 350 to 400 square feet, and a liter covers about 10 square meters. Round up to whole cans.
For that example room with one door and two windows, you would paint 366 square feet twice, which is 732 square feet. At 350 square feet per gallon that is just over 2 gallons, so you would buy 2 gallons and a quart.
Worked examples: how much paint for real rooms
Real results from the calculator, two coats at 350 sq ft per gallon unless the row says otherwise.
| Room | Size and openings | Area to paint | Paint | Buy |
|---|---|---|---|---|
| Small bathroom | 8 x 10 ft, 8 ft walls, 1 door | 268 sq ft | 1.5 gallons | 2 gallons |
| Bedroom | 12 x 12 ft, 8 ft walls, 1 door, 1 window | 349 sq ft | 2 gallons, plus 0.8 for the ceiling | 2 gallons, plus 1 gallon of ceiling white |
| Bedroom | 12 x 14 ft, 8 ft walls, 1 door, 2 windows | 366 sq ft | 2.1 gallons | 2 gallons + 1 quart |
| Dark to light, same room | 12 x 14 ft, 3 coats and primer | 366 sq ft | 3.1 gallons, plus 1 gallon of primer | 3 gallons + 1 quart, plus 1 gallon + 1 quart of primer |
| Living room | 15 x 20 ft, 9 ft walls, 2 doors, 3 windows, primer | 545 sq ft | 3.1 gallons, plus 1.6 of primer | 3 gallons + 1 quart, plus 2 gallons of primer |
| Metric bedroom | 4 x 3.5 m, 2.5 m walls, 1 door, 1 window, 10 sq m per liter | 34 sq m | 6.8 liters | 1 x 5 L + 2 x 1 L |
When the math lands on 3 quarts, the calculator rounds up to a full gallon, because a gallon usually costs less than three quarts.
How many coats of paint do I need?
| Situation | Coats | Primer? |
|---|---|---|
| Refreshing the same or a similar color | 1 to 2 | No |
| Changing to a new, similar depth color | 2 | Usually not |
| Going from dark to light | 2 to 3 | Yes, a tinted primer helps |
| Bright reds, yellows and deep colors | 3 | Yes, a gray or tinted primer |
| New drywall or plaster | 2 | Yes, always |
Paint and primer in one products can save a coat on walls in good condition, but they don't replace a real primer on bare drywall, stains or glossy surfaces.
Paint coverage by surface
The coverage printed on the can assumes smooth, primed walls. Rough and porous surfaces soak up more paint, so lower the coverage figure in the calculator when you are painting textured walls, bare brick or fresh plaster. A drop from 350 to 250 square feet per gallon is common on heavy texture.
How much paint for a whole house?
Measure each room and run it through the calculator separately, then add the totals. Rooms with high ceilings, lots of windows or dark existing colors vary so much that a single whole house estimate is rarely accurate. As a rough guide, a typical bedroom needs 2 gallons for two coats, a living room 2 to 3 gallons and a small bathroom about 1 gallon.
Planning a bigger refresh? Our guides to budget home improvement projects and living room decor ideas are full of ideas, and the flooring calculator helps you plan the floor.
