Free everyday calculator
Estimate wall area, paint volume, and whole gallon cans for a rectangular room.
Result
Enter values and calculate.
How this calculator works
The calculator finds the area of all four walls, subtracts doors and windows, multiplies by the number of coats, then divides by the selected paint coverage.
Worked example
A 12 × 10 × 8 ft room with 40 sq ft of openings and two coats needs about 1.78 gallons at 350 sq ft per gallon, so buy two one-gallon cans.
Frequently asked questions
Does this include the ceiling?
No. This estimate covers four walls only. Add ceiling area to the openings adjustment as a negative value is not supported; calculate it separately.
How much coverage does paint provide?
Many paints cover roughly 350–400 square feet per gallon per coat; use the value printed on your product.
Should I buy exactly the calculated amount?
Buying whole cans and a small margin is practical for texture, waste, and later touch-ups.