How to use the Paint Calculator
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The formula
Paintable area = wall area − doors − windows (US: 20 and 15 sq ft; metric: 1.9 and 1.4 m²); paint = area × coats ÷ coverage
Examples
- 14 by 12 ft room, 8 ft ceiling, 2 coats
Paintable wall area: 366 sq ft Paint needed: 2.09 gallons (buy 3) For 2 coat(s) at 350 sq ft per gallon.
- 20 by 15 ft room, 9 ft ceiling, 2 doors, 4 windows
Paintable wall area: 530 sq ft Paint needed: 3.03 gallons (buy 4) For 2 coat(s) at 350 sq ft per gallon.
- 10 by 10 ft room, one coat, 400 sq ft per gallon
Paintable wall area: 285 sq ft Paint needed: 0.71 gallons (buy 1) For 1 coat(s) at 400 sq ft per gallon.
Limitations and assumptions
Walls only. Add ceilings, trim and primer separately.
Frequently asked questions
How do I calculate paint for a room?
Add the wall lengths and multiply by the height, subtract doors (about 20 sq ft) and windows (about 15 sq ft), then multiply by the coats and divide by the coverage per gallon.
How much does a gallon cover?
Roughly 350 square feet, so check the can.
Does it include the ceiling?
No, only the walls. Calculate the ceiling as length × width and add it.
Should I round up?
Yes, buy the next whole gallon so a batch matches.