Paint Calculator
Calculate gallons of paint needed for any room, accounting for doors and windows.
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Quick Tip
Enter the room length, width and wall height in feet.
About This Tool
Why use Paint Calculator?
Enter your room dimensions, the number of doors and windows and how many coats you plan, and this calculator returns the gallons and litres of paint you need. It works out the wall area from the perimeter and height, subtracts 20 sq ft per door and 12 sq ft per window, and assumes coverage of 350 sq ft per gallon.
A 12 ft × 14 ft room with 8 ft walls has 416 sq ft of gross wall area. Take off one door and two windows and 372 sq ft remain, which is about 1.06 gallons per coat, or 2.1 gallons for two coats. Buy the next size up: paint left over is far less trouble than a second trip mid-job, and a touch-up tin is useful later.
Key Benefits
Doors and windows deducted
20 sq ft per door and 12 sq ft per window come off the total, which is what stops the estimate running high.
Gross and net area shown
Seeing both makes it easy to adjust when your openings are larger than the standard allowances.
Gallons and litres
Coverage is based on 350 sq ft per gallon, with the litre equivalent for metric tins.
How to use Paint Calculator
- 1
Enter the room length, width and wall height in feet.
- 2
Enter how many doors and windows the room has.
- 3
Choose the number of coats — two is normal, three when covering a dark colour.
- 4
Read the gallons and litres needed, then round up to the nearest tin size.
Best use cases
Buy the right amount of paint for a room repaint.
Budget a whole-house job room by room.
Work out extra paint needed for a third coat over a dark wall.
Check a decorator's materials estimate.
Paint Calculator FAQs
How much wall does a gallon of paint cover?
About 350 square feet for one coat on a smooth, primed surface. Textured, porous or previously unpainted walls can drop that to 250–300.
How many coats do I need?
Two for most repaints. Use three when going light over dark, and prime first when covering bare plaster, filler or a strong colour.
Does this include the ceiling?
No, the calculation covers walls only. For the ceiling, use length × width as its own area and add it separately.
Should I buy extra paint?
Yes — round up to the next tin. Touch-ups later are much easier with paint from the same batch, since colour can vary slightly between mixes.
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