Paint Calculator

Find out how many gallons and quarts of paint to buy for a room, based on wall size, openings, coats and coverage.

Each door deducts about 21 sq ft (3 × 7 ft)
Each window deducts about 15 sq ft (3 × 5 ft)
sq ft/gal
Most interior paints cover 350–400 sq ft per gallon per coat

How to use the Paint Calculator

  1. Enter the room length and pick its unit.
  2. Enter the room width and pick its unit.
  3. Enter the wall height and pick its unit.
  4. Enter the number of doors – Each door deducts about 21 sq ft (3 × 7 ft).
  5. Enter the number of windows – Each window deducts about 15 sq ft (3 × 5 ft).
  6. Tick Paint the ceiling too if it applies.
  7. Enter the number of coats.
  8. Enter the coverage per gallon – Most interior paints cover 350–400 sq ft per gallon per coat.
  9. Press Calculate. The result updates automatically as you type, and you can switch the result unit at any time.

About the Paint Calculator

Most rooms need two coats for even color, especially when changing colors or painting over patched drywall. New unprimed drywall soaks up paint, so prime first or use a lower coverage figure such as 300 sq ft per gallon. Textured walls, dark colors and brick can also cut coverage noticeably.

Trim, doors and cabinets are usually painted in a separate semi-gloss sheen; a quart typically covers the trim of an average bedroom.

Formula

Wall area = 2 × (Length + Width) × Height − doors × 21 ft² − windows × 15 ft²
Gallons = Area × Coats ÷ Coverage per gallon

The ceiling (Length × Width) is added when selected. Coverage defaults to 350 sq ft per gallon, the low end of the 350–400 sq ft range printed on most paint cans, to allow for rough or porous surfaces. The result is rounded up to whole quarts.

Example calculation

Using the default values:

  • Room length = 14 ft
  • Room width = 12 ft
  • Wall height = 8 ft
  • Number of doors = 1
  • Number of windows = 2
  • Number of coats = 2
  • Coverage per gallon = 350 sq ft/gal

the calculator returns:

  • Paint needed: 2.09 gallons
  • Buy: 2 gallons + 1 quart
  • Paintable area (one coat): 365 ft²
  • Paint needed (metric): 7.9 L

Frequently asked questions

How much area does a gallon of paint cover?

Typically 350–400 sq ft per coat on smooth, primed walls. Rough, porous or textured surfaces may get only 250–300 sq ft.

How much paint do I need for a 12 × 12 room?

With 8 ft walls, one door and two windows, about 333 sq ft of wall needs roughly 2 gallons for two coats.

Should I subtract doors and windows?

Yes for an accurate estimate. A standard door is about 21 sq ft and an average window about 15 sq ft.

How many quarts are in a gallon?

There are 4 quarts in a US gallon.

Last updated: · Category: Construction calculators

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