Toolivaro

Free Paint Calculator

Estimate how many gallons or liters of paint you need for a room, from wall measurements, openings, and coats.

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Units

Total length of all walls to be painted.

Floor to ceiling (or trim line).

Total area of openings to exclude.

Primer counts as a coat.

Cut-ins, touch-ups, and spills.

Price of one gallon or liter.

How is the result calculated?

Repainting a bedroom: perimeter 60 ft, height 10 ft

A bedroom has walls with a total perimeter of 60 feet and a 10-foot ceiling height, so the gross wall area is 600 sq ft. The two windows and the door total about 21 sq ft of openings, leaving 579 sq ft. With two coats of paint and no waste allowance, the area to paint is 1,158 sq ft. At 350 sq ft per gallon that is about 3.31 gallons — so you should buy 4 gallons.

Input Value
perimeter 60
wallHeight 10
openings 21
coats 2
wastePercent 0
pricePerCan 40
Result 579 sq ft net · 1,158 sq ft to paint · buy 4 gallons · ≈ $160

What is the formula and its assumptions?

Net wall area

wall area = perimeter × wall height − openings

Symbol Meaning
perimeter total length of all walls to be painted
wall height height from floor to ceiling (or trim line)
openings total area of doors, windows, and other non-painted areas

Area to paint

paint area = wall area × coats × (1 + waste%)

Symbol Meaning
coats number of coats (primer counts as a coat)
waste% allowance for cut-ins, touch-ups, and spills

Cans needed

cans = ceil(paint area / coverage per can)

Symbol Meaning
coverage per can 350 sq ft per gallon (≈ 8.6 m² per liter)
ceil rounded up to the next whole can

What are the most common mistakes?

  • Painting the gross wall area without subtracting doors and windows — that can overbuy a full gallon.
  • Forgetting that a second coat doubles the paint, not the coverage.
  • Using the same estimate for walls and ceilings without adjusting the measurements.

What are the assumptions and limitations?

  • Coverage varies with surface texture, sheen, and application method — the estimate is a planning number, not a guarantee.
  • The calculator assumes rectangular walls with a uniform height; cathedral ceilings and irregular layouts need a different model.
  • Buying the next whole can may still fall short on heavily textured or previously unsealed surfaces.

Where do the numbers come from?

Last reviewed August 4, 2026 · Version 1.0.0 · Toolivaro does not guarantee external content.

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Frequently asked questions

Does the coverage rate include primer?

The 350 sq ft per gallon rate is for one coat of finish paint on a sealed, reasonable surface. Primer is a separate coat — enter it in the coats field (for example 3 coats: primer + two finish coats) if you are covering a new surface or a dramatic color change.

Why do I need a waste allowance?

Cutting in around trim, painting over textured surfaces, touch-ups, and spills all consume extra paint. Most painters add 5–10% on top of the calculated area, and buying the next whole can usually covers the difference.

Can I use the same estimate for ceilings?

No — the calculator measures walls using perimeter and height. For a ceiling, use the floor dimensions: length × width gives the ceiling area, then divide by the same coverage rate.

Found a mistake or have a correction? Report it — we review every correction.