Formula
How the paint estimate works
- Wall area = 2 × (room length + room width) × wall height − openings
- Paint volume = wall area × number of coats ÷ product coverage
- Full cans = round paint volume up to the next complete can
Free project planning tool
Paint calculator
Estimate paint volume, full cans, and material cost using your room dimensions and product coverage.
✓ Metric & imperial✓ Transparent assumptions✓ No signup
Walls & roomsInstant estimate
Example calculation
For a 12 × 10 × 8 ft room with 51 sq ft of doors and windows, two coats, and 350 sq ft of coverage per gallon, the estimate is about 3.5 gallons. Buying four 1-gallon cans provides a practical purchase quantity.
Planning tips
- Use the coverage printed on the actual paint label.
- Measure the combined area of doors and windows for a more accurate result.
- Textured or porous walls and dramatic color changes may need more paint.
Common questions
Paint calculator FAQ
How much area does one gallon of paint cover?
Many interior paints cover roughly 350–400 sq ft per gallon for one coat, but the product label is the best value to use.
Should I subtract doors and windows?
Yes. Enter their combined area when you want a tighter estimate. For a quick buffer, you can leave the opening area slightly low.
Does the calculator include primer?
No. Primer coverage varies, so estimate it separately using the same wall area and the coverage printed on the primer label.