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Make It Fit

Painting

Paint Calculator

Work out how many gallons a room takes, once doors, windows and extra coats are accounted for.

Calculate your paint

Room measurements in feet. This estimates wall paint only — ceilings aren't included. The estimate updates as you type.

Room
ft
ft
ft
Coats
coats
Paint
sq ft

Replace this with the coverage stated on your paint can if it differs.

The method

  1. 01

    Wall area

    room perimeter × ceiling height

    Room length and width give the perimeter; ceiling height turns that into wall area. The ceiling itself isn't included.

  2. 02

    Subtract openings

    wall area − door and window areas

    There's no assumed door or window size — measure each one and add it above with "Add a door" or "Add a window".

  3. 03

    Account for coats

    paintable area × number of coats

    Two coats is a common planning assumption, but how many you actually need depends on the paint, the existing surface and color, and the manufacturer's guidance. Bare or patched drywall usually needs a primer coat as well, which this calculator doesn't include.

  4. 04

    Gallons required

    total coverage needed ÷ coverage per gallon

    Uses the coverage rate for your product, then rounds the result up to the next whole gallon, since paint isn't sold in fractions.

Worth knowing

  • Coverage varies by product and surface — use the figure printed on your paint can rather than the calculator's default where they differ.
  • A strong color change may need an extra coat regardless of the arithmetic.
  • Ceilings, trim and primer are calculated separately — they usually take a different product.

Paint calculator example

Room
10 × 12 ft
Ceiling height
8 ft
Door
3 × 7 ft
Window
4 × 3 ft
Coats
2
Coverage per gallon
350 sq ft
  1. Room perimeter2 × (10 + 12) = 44 ft
  2. Gross wall area44 × 8 = 352 sq ft
  3. Door area3 × 7 = 21 sq ft
  4. Window area4 × 3 = 12 sq ft
  5. Openings21 + 12 = 33 sq ft
  6. Paintable wall area352 − 33 = 319 sq ft
  7. Coverage needed (2 coats)319 × 2 = 638 sq ft
  8. Paint required638 ÷ 350 ≈ 1.82 gallons

Buy 2 gallons.

Rounded up from about 1.82 gallons, since paint is bought in whole gallons.

How many coats of paint do you need?

How many coats you actually need depends on more than the arithmetic — the paint manufacturer's instructions, your existing wall color, the new color, the surface's condition and porosity, whether you're priming first, and the paint's own quality, type, and finish all play a part.

Typical coat counts by situation
SituationTypical coats
Similar color, well-prepared surface1–2 coats may be enough, depending on the product
Typical repaint2 coats is a common planning assumption
Large color change or difficult coverageAdditional coats may be needed

Important: these are planning guidelines, not guarantees. Always follow your paint manufacturer's application and coverage instructions for the specific product you're using.

How to calculate paint for a room covers why the ceiling and primer are separate estimates, and how a coverage figure turns into whole containers.

How much area does a gallon of paint cover?

Coverage varies by paint brand, product line, and the surface being painted. Porous or textured surfaces, the application method, how well the surface was prepared, and a significant color change can all reduce real-world coverage compared with the figure on the can — the 350 sq ft per gallon used in the worked example above is only an example, not a universal figure.

The calculator's “Coverage per gallon” field is editable for exactly this reason — replace it with the figure printed on your paint can, or supplied by the manufacturer, so the estimate reflects the product you're actually using.

Should you subtract doors and windows?

Doors and windows reduce the wall surface you're actually painting, so subtracting them gives a more accurate estimate of how much paint you'll need.

For a quick, rough estimate, you can leave small openings out — the result will simply include a little extra paint as allowance. For a more precise figure, enter every door and window you have with “Add a door” or “Add a window” above.

If you're also painting the door itself — not just the wall around it — don't treat it as excluded for that part of the job. That's a separate painting task this calculator doesn't estimate.

Paint calculator FAQ

How do I calculate how much paint I need?
Measure your room's length, width, and ceiling height, add any doors and windows you won't be painting over, choose how many coats you plan to apply, and enter your paint's coverage rate. The calculator above works out the paintable area and rounds the result up to whole gallons.
How many coats of paint should I plan for?
Two coats is a common planning assumption, but the number you actually need depends on the paint, your existing wall color, the new color, and the manufacturer's instructions. See the guidance above, and always check your product's own recommendation.
Should I subtract doors and windows?
Yes, for the most accurate estimate — use "Add a door" or "Add a window" above and enter their actual size. Skipping small openings just adds a little extra allowance to the result.
What coverage per gallon should I use?
Use the figure printed on your paint can or listed in the manufacturer's product information — coverage varies between brands, products, and surfaces. The calculator's "Coverage per gallon" field is editable specifically so you can enter that number.
Does this calculator include ceilings?
No — this calculator estimates wall paint only. Ceiling area isn't included in the result.

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