How do I calculate how much paint I need?

Find the paintable square footage, multiply by the number of coats, add a waste allowance, then divide by the paint coverage per gallon listed on the can.

How many square feet does a gallon of paint cover?

Many interior paints cover about 350 to 400 square feet per gallon on a smooth primed wall. Rough surfaces, strong color changes, and textured walls can reduce coverage.

Should I subtract windows and doors when estimating paint?

For a tighter estimate, subtract large doors and windows. For small projects, many people leave them in the estimate because the extra paint helps cover touch-ups and waste.

Home project calculator

Paint Coverage Calculator

Estimate how much paint you need for interior walls using room size, coats, doors, windows, coverage per gallon, and a practical waste allowance.

Paint to buy 2 gallons For 352 sq ft of paintable wall area with 2 coats.

Room size

Room dimensions Known wall area

Room length (ft) Room width (ft) Wall height (ft)

Room wall area is calculated as perimeter × wall height. Ceilings are not included.

Openings and paint

Doors Windows Coats

Coverage per gallon Extra waste/touch-up (%) Price per gallon ($)

Defaults subtract 21 sq ft per door and 15 sq ft per window. Use the coverage printed on your paint can when possible.

How to use this paint calculator

Enter the room length, width, and wall height, or switch to known wall area if you already measured square footage. Add the number of coats, subtract doors and windows if you want a tighter estimate, then adjust coverage and waste for your paint and surface.

Most interior wall projects need two coats. Primer, textured walls, bare drywall, brick, and dramatic color changes can require more paint than a smooth wall in a similar color.

Quick examples

10 × 10 room, 8 ft walls: about 320 sq ft before doors and windows.
12 × 12 room, 8 ft walls: about 384 sq ft before openings.
Accent wall: switch to known wall area and enter width × height for that wall.

FAQ

Does this include ceilings or trim?

No. This estimate is for walls. Calculate ceilings separately with length × width, and estimate trim based on linear feet and the product coverage listed on the trim paint.

Why add extra paint?

A small waste allowance helps cover roller loss, cut-ins, uneven surfaces, future touch-ups, and normal measuring errors. Ten percent is a practical starting point.

Can I buy quarts instead of another gallon?

For small overages, quarts may be cheaper. For larger rooms, buying full gallons is usually safer because color and sheen can vary slightly between batches.