Paint Calculator for Walls
Estimate how much paint you need for interior walls without including trim, cabinets, or other surfaces you are not painting.
Build the Estimate
Measurement controls, project presets, and a material result card for this calculator.
Formula and Assumptions
Wall paint area = room perimeter x wall height - door and window area. Multiply by coats and waste before dividing by coverage.
- The calculator assumes four straight walls.
- Trim, accent walls, and textured surfaces may need separate adjustments.
Worked Example
- 14 ft by 11 ft room
- 9 ft wall height
- 40 sq ft of doors and windows
- 2 coats
The perimeter is 50 ft and the gross wall area is 450 sq ft. After 40 sq ft of openings, two coats require 820 sq ft of coverage.
With 350 sq ft per gallon paint, this wall-only project needs about 2.4 gallons before rounding to containers.
Measurement Tips
- Measure the length of every wall that will receive the wall color.
- Record door and window widths and heights separately for deductions.
- Keep trim, baseboards, and accent walls out of this wall-only estimate.
Buying Notes
- Round up when switching from dark to light colors.
- Plan a separate finish and quantity for trim or doors.
Common Mistakes
- Including the ceiling area in a wall estimate.
- Deducting tiny outlets or switch plates that do not meaningfully change gallons.
Frequently Asked Questions
Is this paint calculator for walls 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.