Paint coverage calculator
Enter the total length of the walls and their height to see how many gallons a room takes, with doors, windows and a second coat accounted for.
Buy this many gallons
2
1.903 gallons for 2 coats over 333.00 sq ft
How to use it
- Measure each wall you're painting and add the lengths together.
- Enter the ceiling height, and count the doors and windows so their area comes off.
- Set the number of coats. Two is normal; three for a big colour change or over a dark wall.
- Read the gallons to buy. The exact figure is below it if you're mixing gallons and quarts.
Worked example
A 12 × 12 ft room with 8 ft ceilings, one door and two windows, two coats of paint covering 350 sq ft per gallon.
Walls total 48 × 8 = 384 sq ft, less 21 for the door and 30 for the windows = 333 sq ft. Two coats is 666 sq ft ÷ 350 = 1.903 gallons, so buy 2 gallons.
How this is calculated
Wall area is the total wall length × height, and each door takes off 21 sq ft and each window 15 sq ft to give the paintable area. Gallons is paintable area × coats ÷ coverage per gallon, and cans rounds that up to the next whole gallon. Ceilings and trim aren't included; run them separately.
wall area = total wall length × height
paintable area = wall area − doors × 21 sq ft − windows × 15 sq ft
gallons = paintable area × coats ÷ coverage per gallon
cans = gallons rounded up to the next whole can. Ceilings and trim aren’t included; run them separately.
Rates, sources and limits
Last reviewed 13 Sep 2026 by the CalcRabbit team. Estimates only, not financial, tax or medical advice.
Frequently asked questions
Should I buy extra?
A little. Rounding up to whole cans usually leaves enough for touch-ups. Textured walls, bare drywall and rough plaster soak up more, so drop the coverage figure to 250 to 300 sq ft per gallon for those.
How much does a ceiling take?
Length × width ÷ coverage, times coats. A 12 × 12 ceiling is 144 sq ft, so one coat is under half a gallon. Ceiling paint is usually one or two coats.
Do I need primer?
On bare drywall, patched areas, glossy surfaces or when going from dark to light, yes, and it needs its own coat's worth of product. Paint-and-primer-in-one products still usually need two coats.
Is it cheaper to buy a 5-gallon bucket?
Per gallon, yes, typically 15% to 25% less. It makes sense from about 4 gallons up, or when several rooms take the same colour.