Paint Calculator

US & Canada

Measure the room, choose your coats, and get the paint you need in gallons and litres, packed into the cans you will actually buy.

Your room

1.How do you want to measure?

2.Size

ft
ft
ft

Each door takes off 20 sq ft and each window 15 sq ft, typical sizes.

3.Coats and coverage

sq ft/gal

Typical. Most tins claim 350 to 400 sq ft per gallon. Use the figure on the tin you are buying, and go lower for rough or bare surfaces.

Paint needed

0 gallons

2 coats

What to buy

Can How many

Largest cans first, then the smallest can that covers the rest. Canadian stores label the same cans 3.78 L and 18.9 L.

How the paint maths works

Paint is sold by volume but used by area, so the sum is area × coats ÷ coverage. The only parts that need care are taking the openings out and using an honest coverage figure.

  • Wall area = distance around the room × wall height
  • Paintable area = wall area + ceiling, minus 20 sq ft per door and 15 sq ft per window
  • Gallons = paintable area × coats ÷ coverage per gallon
  • Litres = gallons × 3.785

Paint for common room sizes

Two coats, 8 ft walls, walls only, with one door and one window taken off, at 350 sq ft per gallon.

Paint needed for common rooms, two coats
Room Wall area Gallons Litres
Small bathroom, 8 × 8 ft 221 sq ft 1.26 4.8
Bedroom, 10 × 10 ft 285 sq ft 1.63 6.2
Bedroom, 12 × 12 ft 349 sq ft 1.99 7.5
Living room, 12 × 16 ft 413 sq ft 2.36 8.9
Large living room, 14 × 20 ft 509 sq ft 2.91 11
Open plan, 20 × 24 ft 669 sq ft 3.82 14.5

Paint by square footage

Gallons and litres of paint by area to cover
Area 1 coat 2 coats 2 coats, litres
200 sq ft 0.57 gal 1.14 gal 4.3 L
400 sq ft 1.14 gal 2.29 gal 8.7 L
500 sq ft 1.43 gal 2.86 gal 10.8 L
600 sq ft 1.71 gal 3.43 gal 13 L
800 sq ft 2.29 gal 4.57 gal 17.3 L
1,000 sq ft 2.86 gal 5.71 gal 21.6 L
1,500 sq ft 4.29 gal 8.57 gal 32.4 L

Buying in Canada? The cans are the same sizes with metric labels: a quart is 946 mL, a gallon is 3.78 L and a pail is 18.9 L. Switch the calculator to metres and litres to measure in metric.

Before you buy

  • Buy the main colour in one go. Tints can vary slightly between batches, so one order avoids a visible change halfway along a wall.
  • Prime bare surfaces. New drywall and patched areas soak up the first coat unevenly. A primer coat is cheaper than a third coat of finish paint.
  • Trim and doors are extra. They usually take a different sheen, and a quart covers the trim in most rooms.
  • Check the tin. Coverage figures differ by product, so put the one printed on yours into the calculator.

Common questions

How much paint do I need for 500 square feet?
At 350 sq ft per gallon, two coats on 500 sq ft takes 2.86 gallons (10.8 litres). In cans, that is 3 × Gallon (3.78 L). One coat is half that.
How much paint do I need for a 12 by 12 room?
With 8 ft walls, one door and one window, a 12 × 12 room has about 349 sq ft of wall. Two coats takes 1.99 gallons, so 2 × Gallon (3.78 L). Add the ceiling and it needs another 0.82 gallons for two coats.
How many litres of paint do I need for a room?
A typical 12 × 12 ft bedroom (3.7 × 3.7 m) has about 32.4 m² of wall once a door and window come off. At about 8.6 m² per litre, two coats takes 7.5 litres, which is two 3.78 L cans. Canadian cans are the US sizes relabelled: 946 mL, 3.78 L and 18.9 L.
How much does a gallon of paint cover?
Most tins claim 350 to 400 sq ft per gallon for one coat on a smooth, primed wall. That is about 8.6 to 9.8 m² per litre. Fresh drywall, bare wood, texture and deep colours all drink more, so this calculator defaults to the cautious 350. Always check the tin you are buying.
Do I need one coat or two?
Two for almost every job. One coat is fine only when you are repainting the same colour over a sound finish. Going dark to light, or covering new drywall, can need a primer plus two coats. Paint and primer in one products help but do not always replace a separate primer on bare surfaces.
How much paint for the whole interior of a house?
It depends on wall area, not floor area. As a rough guide, 3,000 sq ft of wall at two coats takes 17.1 gallons, so 3 × 5 gallon (18.9 L) plus 2 × Gallon (3.78 L) plus 1 × Quart (946 mL). Measure room by room with the calculator for a real number, then buy 5 gallon buckets for the main colour.
How much do doors and windows take off?
This calculator takes off 20 sq ft per door (a standard 3 ft × 6 ft 8 in door) and 15 sq ft per window. Big patio doors or picture windows take off more, so use the area option and subtract them yourself if your room has a lot of glass.
Is it cheaper to buy a 5 gallon bucket?
Usually, once you need about 4 gallons. A 5 gallon bucket tends to cost about the same as four single gallons, so the calculator switches to a bucket at that point. Leftover paint keeps for years if sealed well, and is handy for touch ups.