Paint Calculator by Square Feet
Use this paint calculator to estimate gallons for a room from wall dimensions, ceiling height, openings, coats, and paint coverage.
Build the Estimate
Measurement controls, project presets, and a material result card for this calculator.
Formula and Assumptions
Paintable square feet = 2 x (width + length) x wall height - openings. Gallons = adjusted square feet / coverage per gallon.
- Default coverage is 350 square feet per gallon.
- Openings include doors, windows, built-ins, and areas you will not paint.
Worked Example
- 12 ft by 10 ft room
- 8 ft wall height
- 2 coats
- 350 sq ft per gallon
The room perimeter is 44 ft, so the wall area is 352 sq ft before openings. Two coats make 704 sq ft of paint coverage needed.
At 350 sq ft per gallon, the room needs just over 2 gallons before rounding up for purchase and touch-ups.
Measurement Tips
- Measure each wall width in feet before adding the room perimeter.
- Measure wall height from finished floor to ceiling.
- Subtract large doors, windows, cabinets, or built-ins that will not be painted.
Buying Notes
- Round up to practical gallon or quart combinations.
- Buy all tinted gallons at the same time to reduce color variation.
Common Mistakes
- Forgetting to multiply by the number of coats.
- Using the label coverage for a smooth wall when the surface is textured.
Frequently Asked Questions
Is this paint calculator by square feet exact?
No. It is an estimate based on common project formulas and the assumptions shown on the page. Always confirm package labels and local conditions before buying materials.
Should I add extra material?
Most projects need extra material for cuts, waste, damaged pieces, uneven surfaces, or future repairs. The calculator includes a waste factor where it matters.
Can I print the result?
Yes. Use the print action on the page to keep a simple copy of the inputs, formula, and estimated material list.