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How Much Paint Do I Need?

Estimate how much paint you need for a room. Enter the length, width, and height of the walls (or total square feet), your paint's coverage per gallon, and how many coats you want. The calculator uses total wall area to give you gallons needed.

Room length along one wall.
Room width (other dimension).
Ceiling height.
Optional: enter total wall area to skip length, width, and height.
Check the paint can label; 350 is typical.
Two coats recommended for most jobs.
Result:
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Paint Calculator — FAQ

How is wall area calculated?
We assume four walls: two of length × height and two of width × height. Ceiling and floor are not included. Add those separately if you plan to paint them.
What coverage should I use?
Check the paint can; 350 sq ft per gallon is common. Coverage drops with rough or porous surfaces, so consider buying a bit extra.
Why do I need two coats?
Two coats improve color and durability. One coat is possible for touch-ups or very light color changes.
Can I use this for exterior paint?
Yes. Use the same length, width, and height for the walls you're painting and your product's coverage. Exterior coverage may differ from interior.

How Much Paint Do I Need?

Figuring out how much paint to buy saves time and money. Buying too little means another trip and possible color mismatch; buying too much wastes product. A paint needed calculator uses the total area of your walls and your paint's coverage to recommend gallons.

You need the room's length, width, and ceiling height. Multiply length by height and width by height, double each for the two pairs of opposite walls, then add them for total wall area. Divide that by the coverage per gallon (usually on the label, often around 350 sq ft) and multiply by the number of coats. That's your paint needed in gallons.

Real-world coverage can vary with surface texture, primer, and application. It's wise to round up to the next gallon or add 10–15% for trim and touch-ups. Use the same approach for exterior walls, checking the product's exterior coverage if it differs from interior.

Planning lighting for the same room? Use our Room Lighting Calculator.

People Also Ask

  • How much paint do I need for a 12x12 room?
  • How many coats of paint do I need?
  • What is 350 sq ft coverage per gallon?
  • Can I use a paint calculator for exterior walls?

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Want to learn more?

Read our full guide: How to Calculate Paint Coverage — step-by-step formula, surface-type coverage rates, and a quick-reference chart by room size.

Last updated: February 2026