Paint Calculator

How to calculate how much paint you need

1. Add up the wall area. For a room: 2 × (length + width) × wall height. A 12 × 12 ft room with 8 ft walls: 2 × 24 × 8 = 384 sq ft.
2. Subtract doors and windows. One 20 sq ft door and one 12 sq ft window: 384 − 32 = 352 sq ft.
3. Multiply by the number of coats. Two coats: 704 sq ft.
4. Divide by the coverage on the can. At 350 sq ft per gallon: 704 ÷ 350 = 2.01 gallons.
5. Round up to what the store sells. 2.01 gallons is a little over 8 quarts, so buy 2 gallons and 1 quart.

The calculator does this for every room at once. Add rooms with Add another room or wall; use One wall for an accent wall or Known area for a fence or a surface you have already measured. Open How it’s calculated to see every room’s numbers.

How much paint per room

Two coats at 350 sq ft per gallon, 8 ft walls, one door and one window per room.

Rooms with more doors and windows, built-in shelves or a fireplace need a little less; rooms with high ceilings need more — enter the real wall height.

How far a gallon goes

Coverage is printed on the can and on the manufacturer’s data sheet. For interior wall paint it is typically:

The calculator starts at 350 sq ft per gallon, the low end, so you are more likely to finish with a little left over than to run out in the middle of a wall. If your can says more, choose 400 or 450 or type the exact figure. Rough plaster, textured walls and bare drywall soak up more paint than smooth painted walls.

Coats and primer

• Two coats is the default. Benjamin Moore recommends two coats for full color development; Sherwin-Williams specifies two coats of finish paint in its systems for drywall, wood, plaster and masonry.
• Primer goes on new drywall and bare wood: Sherwin-Williams lists one coat of primer under two coats of paint for new drywall. A coat of primer also helps when you change to a much darker or lighter color. Choose + 1 coat primer; it is shown on its own line, with its own coverage.
• One coat can work when you repaint the same color over clean, sound paint.

Walls and ceiling: two different paints

Ceilings are usually painted with a flat ceiling paint, and walls with an eggshell or satin wall paint, so the calculator gives two separate totals. Choose + Ceiling on a room to include it. The ceiling area is simply length × width.

Buying: gallons, quarts and 5-gallon buckets

Paint is sold in quarts (¼ gallon), gallons and 5-gallon buckets. The calculator rounds up to whole quarts and then packs the order: 5-gallon buckets first, then gallons, then quarts — and when you would need three quarts, it buys a gallon instead. Keep a little of each color for touch-ups, and mix all the cans of one color in a larger bucket before you start (“boxing”) so the shade is even across walls.

Measuring the floor next, for carpet or flooring? The square footage calculator adds up rooms the same way. Replacing walls before painting? The drywall calculator and tile calculator are on the way; for a slab or steps outside, use the concrete calculator, and for bedding around the house the mulch calculator.