Paint Calculator
Enter your total wall length, ceiling height, number of coats, and openings to deduct. Get the paintable area and gallons needed.
Results
- Paint needed
- 3 gal
- Paintable area
- 438 sq ft
- Coverage with coats
- 876 sq ft
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
Painting a room, a whole floor, or the house exterior? This paint calculator turns your wall dimensions into paintable square footage, deducts doors and windows, and tells you how many gallons to buy for the number of coats you plan.
It uses a realistic 350 sq ft per gallon coverage rate, so the estimate matches what you will actually get on primed drywall, not the optimistic number on the can.
Also used as a wall paint estimator, room paint calculator, and interior paint coverage calculator.
How to use the paint calculator
- Enter the total wall length in ft.
- Enter the wall height in ft.
- Enter the number of coats.
- Enter the doors & windows.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Total wall length
- 60 ft
- Wall height
- 8 ft
- Number of coats
- 2
- Doors & windows
- 2
Results
- Paint needed
- 3 gal
- Paintable area
- 438 sq ft
- Coverage with coats
- 876 sq ft
Using the example values above, the paint calculator returns 3 gal (paint needed). Change any field to match your own project and the numbers update instantly.
How much paint do I need for a room?
Measure the total length of every wall, multiply by the wall height, and subtract about 21 sq ft for each door and window. Divide by 350 for one coat, then multiply by the number of coats. A typical 12 × 12 ft room with 8 ft ceilings and two openings works out to roughly 2 gallons for two coats.
Ceilings are usually painted separately with flat ceiling paint: multiply length by width and divide by 350 per coat.
When do you need two coats?
Plan on two coats whenever you change color, paint over a dark shade, or work on new unprimed drywall. A same-color refresh on a wall in good shape can sometimes get away with one coat and a touch-up.
Primer is not optional on new drywall, bare wood, or patched areas. Count primer as its own coat at the same coverage rate.
Formula
Gallons = (paintable area × coats) ÷ 350. Each opening deducts ~21 sq ft.
Frequently asked questions
- How much area does a gallon of paint cover?
- About 350 sq ft per coat on smooth, primed surfaces.
- Do I need two coats?
- Most color changes need two coats; same-color refreshes may need only one.
- How many gallons of paint do I need?
- Divide paintable area by 350 sq ft per coat, then multiply by the number of coats. A 12×12 room usually takes 1–2 gallons for two coats.
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