Paint Calculator

Estimate US gallons for room walls and an optional ceiling, using your paint coverage and coat count.

Use calculatorQuestions & answers

Try an example — choose a starting point, then adjust the inputs.

ft
ft
ft
Use a separate estimate for ceiling paint of a different type or finish.
Use the coverage on your paint label. Trim and primer are excluded.
Paint Needed
2 gallons
for 2 coats

How to Calculate Paint Needed

Wall Area = 2 × (Length × Height) + 2 × (Width × Height)
Paintable = Wall Area − Door Area − Window Area + Optional Ceiling Area
US Gallons = (Paintable × Coats) ÷ Coverage per Gallon

How much paint for a 12x12 room with two coats?

Four 8-foot walls have 2 × (12 + 12) × 8 = 384 sq ft of area. One assumed 20 sq ft door and two assumed 15 sq ft windows leave 334 sq ft. Two coats cover 668 sq ft in total. At 350 sq ft per US gallon, that is 1.91 gallons, rounded up to 2 whole gallons.

Including the ceiling in a 12x12 room

The ceiling adds 12 × 12 = 144 sq ft. With the same openings, paint and two coats, the estimate becomes (334 + 144) × 2 ÷ 350 = 2.73 US gallons, or 3 whole gallons. Choose the walls-plus-ceiling example to try it. If the ceiling has a different finish, keep its purchase separate instead of combining gallons.

Is floor square footage enough to estimate paint?

No. Two rooms with the same floor area can have different perimeters and wall areas. Measure room length, width and wall height, then subtract openings. For differently sized doors or windows, divide their total measured area by their count and enter that average.

Choose the right coverage for your paint

The 350 sq ft default is an example, not a guarantee. Enter the manufacturer's one-coat coverage for the product and surface; see BEHR's measuring and coverage guide for an example. Texture, porosity, application method and color changes affect the amount needed. Primer is a separate product; calculate it separately using its own coverage and coat count.

What is included?

This tool estimates four rectangular walls and, optionally, a flat rectangular ceiling. Door and window areas are editable; trim is excluded. For sloped ceilings or irregular walls, measure them separately. Gallons are US gallons and the purchase estimate rounds up to whole gallons; no additional waste percentage is added.

Use the square footage calculator to check surface areas. For a floor project, use the tile calculator instead.

Frequently Asked Questions

How much paint do I need for a room?
Measure the wall area (length × height of each wall), subtract doors and windows, multiply by the coat count, then divide by the one-coat coverage on the paint label. A typical 12×12 room with 8ft ceilings needs about 2 gallons for two coats.
How many square feet does a gallon of paint cover?
Coverage depends on the product and surface. This calculator starts at 350 square feet per US gallon for one coat; replace that with the coverage on your paint label.
Does the paint calculator include the ceiling?
Choose Walls plus ceiling to add the room length times width. That setting uses the same paint, coverage and coat count for both surfaces. If the ceiling uses a different product or finish, calculate and buy it separately.
Should I subtract doors and windows?
Yes. Enter the number of openings and their average areas. The starting assumptions are 20 sq ft per door and 15 sq ft per window; replace them with your measured sizes.

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