Paint calculator
This is arithmetic on the area, coats and coverage you enter. Real coverage varies with the surface and the painter, so treat it as a buying estimate — it is usually better to have a little left over than to run out mid-wall.
Enter the wall size, how many walls, the coats and the coverage from the tin, and the tool works out the volume of paint and rounds it up to whole cans. Coverage and can size are editable because they change with the product and the surface.
Worked example
Four 12 ft × 8 ft walls are 384 square feet. Two coats is 768 square feet of painting. At 350 ft² per gallon that is 768 ÷ 350 ≈ 2.2 gallons. In 1-gallon cans you would buy 3 and keep the rest for touch-ups.
The formula
paint = (area × coats) ÷ coverage · cans = paint ÷ can size, rounded up
Coverage is stated per unit of paint, so dividing the painted area by it gives the volume directly. Multiply the area by the coats first, since each coat is a full pass over the wall. Rounding up to whole cans is what you actually carry to the till.
Questions
- How much paint do I need for a room?
- Add up the wall area, multiply by the number of coats, and divide by the coverage on the tin. A gallon typically covers around 350 square feet per coat, so a 400 sq ft room in two coats needs about 800 ÷ 350 ≈ 2.3 gallons. This tool does that and rounds up to whole cans.
- How many coats should I plan for?
- Two is the honest default and what this tool assumes unless you change it. One coat rarely covers evenly, especially over a colour change or fresh drywall. A big colour shift or bare, thirsty surfaces can want a primer coat on top of that, so add it to the coat count.
- What coverage should I use?
- The tin states it, and it is the number that most affects the answer, so it is an editable field here. Smooth, sealed walls give the most coverage; rough, porous or textured surfaces drink paint and cut it down. When in doubt, use the lower end of the range on the can.
- Should I subtract doors and windows?
- For a rough estimate you can leave them in — the extra paint covers touch-ups and a second dip of the roller. If you are counting pennies on an expensive paint, subtract the big openings from the area you enter and you will buy a can or two less.
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