Paint calculator
Work out how much paint a room needs after doors and windows, and which quart, gallon or 5-gallon cans to buy.
Floor to ceiling. 8 ft 6 in is 8.5 ft.
A whole number from 1 to 10. Use the number on your can.
Results
- Paint needed
- 1.99 galCoats: 2, coverage 350 sq ft/gal
- Area to paint
- 349 sq ft
- Cans to buy
- 2 × 1 gal0.01 gal left over
Coverage, door and window sizes
Use the figure on your can. Rough, porous or bare walls take more paint.
Every door and every window is counted at these sizes. Measure one of each, frame included if you will not paint it.
Cans in the mix: 1 qt, 1 gal, 5 gal. The mix is the fewest cans that hold enough paint without leaving more than a 1 gal can over.
Estimate only. Check product labels and local building rules before you buy or build.
Quick answer
Add up the wall area (room perimeter × wall height), subtract the doors and windows, multiply by the number of coats and divide by the coverage on the can, usually 350 to 400 sq ft per gallon. A 12 × 12 ft room with 8 ft walls, one door and one window has 349 sq ft of wall, so two coats at 350 sq ft per gallon take 1.99 gallons: two 1-gallon cans.
How to use the paint calculator
- Choose Room size and type the length and width of the floor and the wall height, or choose Wall area if you have already added up the walls you will paint.
- Enter the number of doors and windows. Each door counts as 36 × 80 in (20 sq ft) and each window as 36 × 60 in (15 sq ft); change those sizes under Coverage, door and window sizes.
- Set the number of coats and choose Walls and ceiling if the ceiling is painted too. The ceiling gets its own cans, so you can buy a different color or product for it.
- Check the coverage against the label on your can. The calculator starts at 350 sq ft per gallon, the low end of the 350 to 400 sq ft that Sherwin-Williams gives for a gallon.
How do you calculate how much paint you need?
Find the wall area, take off the doors and windows, multiply by the number of coats and divide by the coverage per gallon. For a rectangular room the wall area is the perimeter, 2 × (length + width), times the wall height. Door and window sizes in inches turn into square feet when you divide width × height by 144.
The suggested cans are the fewest that hold enough paint without leaving more than one gallon over. That is why 3.6 gallons becomes four 1-gallon cans, while 4.2 gallons becomes one 5-gallon pail.
wall area = 2 × (length + width) × wall heightdoor area (sq ft) = width (in) × height (in) ÷ 144area to paint = wall area − doors × door area − windows × window areaceiling area = length × widthpaint (gal) = area to paint × coats ÷ coverage (sq ft per gal)How much paint do I need for a 12×12 room?
A 12 × 12 ft room with 8 ft walls, one door and one window needs 1.99 gallons for two coats on the walls: two 1-gallon cans. Every row below uses the same assumptions: 8 ft walls, one 36 × 80 in door, one 36 × 60 in window, two coats and 350 sq ft per gallon.
| Room (ft) | Walls (sq ft) | Paint (gal) | Cans to buy |
|---|---|---|---|
| 10 × 10 | 285 | 1.63 | 2 × 1 gal |
| 10 × 12 | 317 | 1.81 | 2 × 1 gal |
| 12 × 12 | 349 | 1.99 | 2 × 1 gal |
| 12 × 14 | 381 | 2.18 | 2 × 1 gal + 1 × 1 qt |
| 14 × 16 | 445 | 2.54 | 3 × 1 gal |
| 16 × 20 | 541 | 3.09 | 3 × 1 gal + 1 × 1 qt |
Walls only, computed with the calculator. Ceilings add 0.57, 0.69, 0.82, 0.96, 1.28 and 1.83 gallons for the same rooms: one 1-gallon can up to 12 × 14 ft, two for the larger rooms.
Worked examples
A 12 × 12 ft bedroom, walls and ceiling
The walls are 2 × (12 + 12) × 8 = 384 sq ft. One door (36 × 80 in = 20 sq ft) and one window (36 × 60 in = 15 sq ft) leave 349 sq ft to paint. Two coats at 350 sq ft per gallon take 349 × 2 ÷ 350 = 1.99 gallons, so buy two 1-gallon cans.
The ceiling is 12 × 12 = 144 sq ft. Two coats take 144 × 2 ÷ 350 = 0.82 gallons, one more 1-gallon can. In all you paint 493 sq ft with 2.82 gallons.
A living room and hall measured as one wall area
The walls of an open living room and hallway add up to 1,000 sq ft, with 3 doors and 4 windows. The openings take off 3 × 20 + 4 × 15 = 120 sq ft, which leaves 880 sq ft. Two coats at 350 sq ft per gallon take 880 × 2 ÷ 350 = 5.03 gallons.
The calculator suggests one 5-gallon pail and one quart, with 0.22 gallons left over. A 5-gallon pail and a 1-gallon can is also two cans, but it would leave almost a gallon unused.
How many square feet does a gallon of paint cover?
A gallon of interior wall paint covers about 350 to 400 sq ft, according to Sherwin-Williams, and the calculator reads that as the area one coat covers. Benjamin Moore lists 400 to 450 sq ft for its Regal Select matte. Primer covers less, about 200 to 300 sq ft per gallon. Use the figure on your own can when you have it.
| Can | Holds | One coat covers |
|---|---|---|
| 1 quart | 0.25 gal (0.95 L) | 88 to 100 sq ft |
| 1 gallon | 1 gal (3.79 L) | 350 to 400 sq ft |
| 5-gallon pail | 5 gal (18.93 L) | 1,750 to 2,000 sq ft |
Sherwin-Williams sells its Duration Home interior paint in these three sizes and puts a quart at about 100 sq ft.
Do I need one or two coats of paint?
Plan on two coats unless the can says one is enough for your wall. Benjamin Moore lists 1 or 2 recommended coats for its Regal Select and Ultra Spec 500 interior paints, and its own paint calculator assumes two coats on walls. The calculator starts at two so the estimate does not come up short.
If you are covering a strong color, fresh patches or bare drywall, follow the primer and coat advice on the label and set Coats to match. For a primer coat, set Coats to 1 and Coverage to the primer’s own figure.
Questions
How much paint do I need for a 12x12 room?
About 2 gallons for the walls. A 12 × 12 ft room with 8 ft walls has 384 sq ft of wall, and 349 sq ft is left after one door and one window. Two coats at 350 sq ft per gallon take 1.99 gallons, so two 1-gallon cans. Painting the 144 sq ft ceiling as well adds 0.82 gallons, which is one more 1-gallon can.
How much paint do I need for a ceiling?
About 1 gallon for a 12 × 14 ft ceiling. The ceiling is 168 sq ft, and two coats at 350 sq ft per gallon take 0.96 gallons, so one 1-gallon can. To work out your own, multiply the room length by its width, then by the number of coats, and divide by the coverage per gallon. Choose Walls and ceiling in the calculator to see the ceiling cans listed apart from the wall cans.
How many square feet does a quart of paint cover?
About 100 sq ft for one coat. Sherwin-Williams puts a quart at about 100 sq ft, a quarter of the 350 to 400 sq ft a gallon covers. That is one coat on a 10 × 10 ft wall, or two coats on a 50 sq ft accent wall. Four quarts hold the same paint as one gallon, so for anything larger buy gallons and compare the price per gallon.
How much primer do I need?
Plan on one gallon of primer for every 200 to 300 sq ft, the range Sherwin-Williams gives for primer. To use the calculator for primer, set Coats to 1 and Coverage to the figure on the primer can, for example 250 sq ft per gallon. The 349 sq ft of walls in a 12 × 12 ft room then need 1.4 gallons, or two 1-gallon cans.
Should I buy a 5-gallon bucket or single gallons?
Buy a 5-gallon pail once you need 4 gallons or more of one color. The calculator picks the fewest cans that leave no more than one gallon over, so 3.6 gallons becomes four 1-gallon cans and 4.2 gallons becomes one 5-gallon pail. Compare the pail price with four or five single gallons at your store before you choose.
Sources
- Sherwin-Williams, Paint Calculator (checked October 19, 2026)A gallon of paint covers about 350 to 400 sq ft, a quart about 100 sq ft, a gallon of primer about 200 to 300 sq ft.
- Sherwin-Williams, Duration Home Interior Acrylic Latex Paint (checked October 19, 2026)Sold in 1 quart, 1 gallon and 5 gallon containers.
- Benjamin Moore, Regal Select Interior Paint, Matte (checked October 19, 2026)Coverage 400 to 450 sq ft per gallon, 1 or 2 recommended coats, sold by the quart and gallon.
- Benjamin Moore, Ultra Spec 500 Interior Paint, Flat (checked October 19, 2026)Coverage 350 to 400 sq ft per gallon, 1 or 2 recommended coats.
- Benjamin Moore, Paint Calculator (checked October 19, 2026)The calculator assumes 2 coats of paint and does not include the ceiling.
Spotted a mistake?
Tell us which numbers you used and what you expected. We read every message. Contact us