Paint Calculator: How Much Paint Do I Need?
Estimate interior wall area, how many gallons of paint you need and paint material cost from room dimensions, doors, windows, coats and coverage.
Your project details
Change the assumptions below to match your project.
The room size is not the paintable area
The calculator estimates the four walls from room length, width and wall height. It then subtracts a simple door/window allowance, multiplies by coats and divides by the coverage figure you enter.
Worked example: 14 × 12 ft room, 8 ft walls
The room perimeter is 52 ft. Multiply by 8 ft and gross wall area is 416 sq ft. If one door and two windows remove about 51 sq ft, net wall area is roughly 365 sq ft. Two coats create about 730 sq ft of coverage demand.
Coverage is a product input, not a universal constant
The default 350 sq ft per gallon is only a starting assumption. Use the coverage shown on the product's current label or technical data. Rough masonry, new drywall, porous surfaces and major color changes can use more coating than a smooth previously painted wall.
Primer belongs on its own line
Primer may be appropriate for new drywall, stains, repaired areas, glossy surfaces or difficult color changes. If primer is required, calculate it separately rather than treating it as another finish coat.
Ceilings, trim and doors are separate scopes
| Surface | How to plan it |
|---|---|
| Walls | Perimeter × wall height, less openings as appropriate |
| Ceiling | Room length × width |
| Baseboards / trim | Linear feet plus product-specific coverage |
| Doors | Count and face area; product may differ from wall paint |
What the calculator does not price
It estimates paint material only. Professional painting quotes may include patching, sanding, caulking, masking, furniture moving, ceiling work, trim, doors, primer, cleanup and multiple mobilizations.
Older-home safety
If the project disturbs painted surfaces in a pre-1978 home, review applicable lead-safe requirements before sanding, scraping or demolition. The U.S. EPA's Renovation, Repair and Painting program is the relevant federal starting point.
Related reading
See How Much Paint Do I Need for a Room? and Interior Painting Cost per Square Foot.
Measure surfaces before pricing the room
- Enter the room dimensions and openings. Floor area alone does not tell you paintable wall area.
- Use the product's real coverage. Coverage, coats and primer needs should come from the paint you are actually buying.
- Keep other surfaces separate. Ceilings, trim, doors and repair work should not be hidden inside the wall-paint result.
Paint calculator reference
Formula
Paintable wall area ≈ perimeter × wall height − openings. Multiply by coats, then divide by the selected product coverage.
Keep separate
Primer, ceilings, trim, doors and major repair work should be calculated or priced outside the wall-paint result.
Best input
Use the actual product's stated coverage and price instead of a generic gallons-per-room shortcut.
On this page
Calculator · Room quantity guide · Quote comparison · Whole-house workflow