Paint
calculator.
Find how much paint to buy for a room or a wall: the wall area less doors and windows, times the number of coats, divided by the coverage on the can. The answer is rounded to gallons and quarts, or to liter cans, with the ceiling and primer counted separately.
340 sq ft of wall at 2 coats needs 1.94 gal (7.4 L) of paint, so buy 2 gallons.
- Wall paint to buy
- 2 gallons
- Wall paint needed
- 1.94 gal (7.4 L)
- Wall area to paint
- 340 sq ft (384 sq ft − 44 sq ft of doors and windows)
wall area = 2 × (12 + 12) × 8 − 44 = 340 sq ft; paint = 340 × 2 ÷ 350 sq ft/gal = 1.9428571 galMeasure once,
buy the right cans.
- Wall area = 2 × (length + width) × height, less each door and window. The defaults take off 20 sq ft per door (36 × 80 in) and 12 sq ft per window (3 × 4 ft); change them to your own sizes.
- Paint = area × coats × (1 + extra ÷ 100) ÷ coverage per coat. The ceiling and primer are worked out separately because they are usually different products.
- U.S. cans: whole gallons, then quarts for the rest. If three or more quarts would be needed, one gallon is suggested instead, unless your prices make the quarts cheaper.
- Liter cans: the fewest 10, 5, 2.5 and 1 L cans that leave less than 1 L over.
- 1 US gallon = 3.785411784 L and 1 sq ft = 0.09290304 m², so 350 sq ft per gallon equals 8.59 m² per liter.
How do you calculate how much paint you need?
Work out the wall area, take off the doors and windows, multiply by the number of coats and divide by the coverage on the can. A 12 × 12 ft bedroom with 8 ft walls has 2 × (12 + 12) × 8 = 384 sq ft of wall. Less one door (20 sq ft) and two windows (24 sq ft) that is 340 sq ft. Two coats at 350 sq ft per gallon is 680 ÷ 350 = 1.94 gallons, so buy 2 gallons.
wall area = 2 × (length + width) × height − doors − windows
gallons = wall area × coats ÷ coverage per gallonHow many square feet does a gallon of paint cover?
Sherwin-Williams says a gallon of paint typically covers about 350 to 400 sq ft, and a gallon of primer about 200 to 300 sq ft. Benjamin Moore lists 400 to 450 sq ft per gallon for its Regal Select interior paint. Those figures are per coat on a smooth, sealed wall. Textured plaster, bare drywall and spraying use more, so use the low end of the label range or add an extra allowance. The calculator starts at 350, the cautious end of the typical range.
How many coats of paint do you need?
Two coats is the usual plan for walls, and Benjamin Moore lists one or two coats for its Regal Select paint. A big color change, a dark color over a light one or bare new drywall may need a coat of primer first, or a third coat. On the 340 sq ft bedroom, a third coat takes the paint from 1.94 to 2.91 gallons, which is 3 gallons.
Should you buy gallons or quarts?
A quart is a quarter of a gallon. If the job needs 2.09 gallons, two gallons and one quart cover it. If it needs 1.6 gallons, the remainder would take three quarts, and one more gallon is usually the better buy and leaves paint for touch-ups. Enter both prices and the calculator compares them for you. For a large job, 5-gallon pails are often cheaper per gallon than single cans.
How much paint do you need for a ceiling?
The ceiling area is the floor area: length × width. A 14 × 12 ft ceiling is 168 sq ft; two coats at 375 sq ft per gallon is 0.9 gallons, so one gallon. Ceiling paint is usually a separate flat product, so the calculator gives it its own line instead of adding it to the wall paint.
Worked examples.
Bedroom walls, two coats
A 12 × 12 ft room with 8 ft walls, one door and two windows, at 350 sq ft per gallon.
2 gallons
Load this exampleWalls, ceiling and primer
A 14 × 12 ft room with 9 ft walls, two doors and three windows, 375 sq ft per gallon, primer at 250, $40 a gallon and $16 a quart.
2 gallons + 1 quart · ceiling 1 gallon
Load this exampleOne accent wall
A 12 × 8 ft wall, two coats at 400 sq ft per gallon.
2 quarts
Load this exampleTextured walls, three coats
500 sq ft of wall, a strong color change in three coats at 400 sq ft per gallon, plus 10% for texture.
4 gallons + 1 quart
Load this exampleMetric room with ceiling
A 5 × 4 m room with 2.7 m walls, one door (1.9 m²) and one window (1.1 m²), two coats at 9 m² per liter, €10 a liter.
1 × 10 L + 1 × 1 L · ceiling 1 × 5 L
Load this exampleWhat this calculator
does not do.
- Coverage comes from the can or data sheet you enter. Real coverage depends on the surface, the color change, the tool and how thickly the paint goes on, so treat the result as a buying estimate.
- Door and window sizes are typical defaults; enter your own if they differ. Trim, doors and window frames that you will paint need their own estimate, usually in a different product.
- It treats the room as a rectangle with walls of one height. For sloped ceilings, stairwells or gables, add up the wall areas yourself and use Total wall area.
- Can sizes and prices vary by brand and country; 5-gallon pails and other sizes are not included in the rounding.
Common questions.
How much paint do I need for a 12 × 12 room?
With 8 ft walls, one door and two windows, the walls are 340 sq ft. Two coats at 350 sq ft per gallon need 1.94 gallons, so buy 2 gallons. Add a gallon if you are painting the 144 sq ft ceiling too.
How many square feet does a gallon of paint cover?
About 350 to 400 sq ft per coat for typical interior paint, according to Sherwin-Williams. Check your product's label or data sheet; some list more, and rough surfaces get less.
Do I subtract doors and windows when calculating paint?
Yes, for the wall paint. A 36 × 80 in door is 20 sq ft and a 3 × 4 ft window is 12 sq ft. Painting the doors and trim is a separate job, usually in a different sheen.
How many gallons of paint for two coats?
Twice what one coat needs. 340 sq ft at 350 sq ft per gallon is 0.97 gallons per coat, so 1.94 gallons for two.
How much does a quart of paint cover?
A quarter of a gallon's coverage: about 88 to 100 sq ft per coat for paint rated at 350 to 400 sq ft per gallon.
- Sherwin-Williams: Paint calculator — a gallon of paint typically covers about 350–400 sq ft; a gallon of primer about 200–300 sq ft
- Benjamin Moore: Regal Select Interior Paint, Matte — coverage 400–450 sq ft per gallon; 1 or 2 recommended coats
- NIST Guide to the SI, Appendix B.9: conversion factors — US gallon and liquid quart to cubic meters; 1 ft² = 0.09290304 m² exactly
Areas are converted with exact NIST factors into the unit of the coverage figure, so a room measured in meters can use a coverage given in sq ft per gallon and the other way round. Paint is worked out per product (walls, ceiling, primer) and rounded to cans only at the end. Tests cover hand-worked rooms, the quart-or-gallon rule with and without prices, the metric can rule, 300 random rooms checked for unit independence, can plans that always cover the need with less than one gallon or one liter over, and every invalid input.
Built and reviewed by CalculatorLab against the sources above; every worked example on this page is re-checked by our automated test suite before each release. How we build and check calculators. Found a problem? Tell us.