Paint needed = area to paint × number of coats ÷ coverage per coat. The calculator works out the wall area from the room size, subtracts doors and windows, can add the ceiling, and turns the total into cans you can actually buy.
It picks the cheapest mix of package sizes, for example one 5-gallon bucket plus a gallon instead of six gallons.
How to use
- Enter the room length, width and wall height, or measure wall by wall.
- Set the number of doors and windows. Tick the ceiling if you're painting it too.
- Choose the number of coats: 2 is standard; 3 for strong color changes.
- Check the coverage on your paint can and type it in if it differs.
How far each can goes
| Can | 1 coat | 2 coats | 3 coats |
|---|---|---|---|
| 5 gal | 2,000 sq ft | 1,000 sq ft | 667 sq ft |
| 1 gal | 400 sq ft | 200 sq ft | 133 sq ft |
| 1 qt | 100 sq ft | 50 sq ft | 33 sq ft |
At 400 sq ft/gal per coat. Rough, porous or unprimed surfaces take more.
Paint coverage
Interior wall paint usually covers 350 to 400 sq ft per gallon per coat; Benjamin Moore lists 400 to 450 for Regal Select. In metric, 10 m² per liter per coat is a safe default. The calculator uses about 400 sq ft per gallon; change it to the number on your can.
Doors, windows and ceiling
A standard door is about 21 sq ft and a window about 15 sq ft. The ceiling of a 12 × 12 ft room is 144 sq ft. Ceilings often take a different, flat paint, so you can calculate them separately.
Where the numbers come from
Coverage and consumption figures come from manufacturer data sheets and published standards: