Paint Calculator
Enter the size of the room and get the paint you need in gallons or litres — with doors, windows, ceiling and the number of coats taken into account.
- Walls and ceiling
- Coats
- Cans to buy
- Private
Printed on the can. Typical: 10–12 m² per litre, 350–400 ft² per gallon.
Cost (optional)
Leave at 0 to skip the cost.
How to calculate paint for a room
Measure once, buy once.
- 1
Enter the room size
Length, width and wall height in feet or metres.
- 2
Subtract openings
Enter the number of doors and windows; tick the ceiling if you are painting it too.
- 3
Set coats and coverage
Two coats is the usual choice. Check the coverage printed on the can, then read the quantity and the cans to buy.
No half-empty cans, no second trip
A realistic estimate for interior walls and ceilings.
Walls and ceiling
Wall area from the room’s perimeter and height, plus the ceiling if you want.
Openings subtracted
Standard doors and windows are deducted for each one you enter.
Coats and coverage
Set the number of coats and the coverage from your product’s label.
Cans to buy
The quantity is turned into a sensible mix of can sizes.
Cost estimate
Enter the price per gallon or litre to see what the job will cost.
Link to your calculation
Copy a link that reopens the calculator with your numbers filled in — handy for sharing or saving a scenario.
Made for phones
Large fields, the right keyboard for numbers and a layout that fits small screens.
Private by design
Everything is calculated in your browser. Your numbers are not sent to a server.
How much paint do I need?
The paintable wall area is the room’s perimeter times the wall height, minus doors and windows: 2 × (length + width) × height − openings. A 16 × 12 ft room with 8 ft walls has 2 × 28 × 8 = 448 ft² of wall; with one door (about 21 ft²) and one window (about 15 ft²) that leaves 412 ft².
Divide the area by the paint’s coverage and multiply by the number of coats. A gallon of interior wall paint covers about 350–400 ft² (a litre about 10–12 m²) on smooth, primed walls. Two coats on the example room need 412 × 2 ÷ 350 ≈ 2.4 gallons, so buy two gallons and two quarts.
Coverage drops on rough, porous or unprimed surfaces such as new drywall, textured plaster or bare wood, and when you paint a light colour over a dark one. In those cases use a primer first and allow 10–20 % more paint. Trim, doors and built-ins are usually painted with a different product and should be estimated separately.
Paint for two coats on walls (8 ft / 2.4 m ceilings)
| Room | Wall area | Paint for two coats |
|---|---|---|
| Bathroom 5 × 8 ft | ≈ 170 ft² (16 m²) | 1 gallon (3–4 L) |
| Bedroom 10 × 12 ft | ≈ 315 ft² (29 m²) | 2 gallons (6 L) |
| Living room 14 × 18 ft | ≈ 475 ft² (44 m²) | 3 gallons (9–10 L) |
| Open-plan 20 × 24 ft | ≈ 670 ft² (62 m²) | 4 gallons (13–15 L) |
Tips
- Replacing the floor after painting? Estimate it with the Flooring Calculator.
- Tiling a bathroom or kitchen wall instead? Use the Tile Calculator.
- Painting an odd-shaped tank or object? The Volume Calculator also gives surface areas.
- Buy all the paint for a room in one go and mix the cans together in a bucket: colour can vary slightly between batches.
Frequently asked questions
Can’t find your answer? Contact us — we reply quickly.
How much paint do I need for a 12 × 12 room?
With 8 ft ceilings, one door and one window the walls are about 350 ft². Two coats need roughly 2 gallons (7–8 litres), plus about half a gallon if you paint the ceiling.
How many square feet does a gallon of paint cover?
About 350–400 ft² per coat on smooth, primed walls. A litre covers about 10–12 m². Always check the label of your product.
Do I need two coats?
Usually yes. Two coats give an even colour and a durable finish; one coat can be enough when refreshing the same colour with a high-quality paint.
Should I subtract doors and windows?
Yes for an accurate figure. The calculator deducts about 21 ft² (1.9 m²) per door and 15 ft² (1.4 m²) per window. For very large windows, reduce the wall area further.
How much paint does a ceiling need?
The ceiling area is length × width. A 12 × 12 ft ceiling is 144 ft², so one coat takes a little under half a gallon.
Are my numbers stored or sent anywhere?
No. The calculation runs in your browser. Your last inputs are remembered on your own device only, so the form is still filled in when you come back; use Reset to clear them.
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