Room Paint Needed Calculator
Estimate how much paint you need for walls and ceilings, including coats.
About Room Paint Needed Calculator
Paint is sold by volume but used by area, so the calculation runs area first. The walls of a rectangular room are the perimeter - twice the length plus the width - multiplied by the ceiling height, which is why a long thin room takes more paint than a square one of the same floor area. Doors and windows come off at roughly 20 square feet each, and the ceiling goes on only if you are painting it. Divide the result by the spread rate on the can and multiply by the number of coats. Two coats is the normal answer rather than a luxury: one coat of most colours over a different base leaves a patchy, translucent finish. Buy in whole cans and expect the last one to be part-used - it is worth keeping for touch-ups, since a later batch will not match exactly. Under-buying is the expensive mistake, because a second trip usually means a different batch and a visible seam where the two meet.
Formula
Room Paint Needed
Wall area = 2 x (length + width) x height, plus the ceiling if painted, less 20 sq ft per opening; paint = area x coats / spread rate
- Spread rate
- Square feet one gallon covers in a single coat, printed on the can - 350 is typical for latex on primed drywall
- 20 sq ft
- A standard 3 ft by 6 ft 8 in door; an average window is a little less, so the two balance out
- Coats
- Each coat needs its own full quantity, so two coats doubles the paint
Worked example
With the default values below, Room Paint Needed Calculator returns Paint Needed of 1.67. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Room lengthaccepts 0–200 ft
- 12 ft
- Room widthaccepts 0–200 ft
- 10 ft
- Ceiling heightaccepts 0–30 ft
- 8 ft
- Coatsaccepts 1–5
- 2
- Doors and windowsaccepts 0–50
- 3
- Spread rateaccepts 50–600 sq ft
- 350 sq ft
- Painting the ceiling too
- No
Results
- Paint Needed
- 1.67 gal
- 1-Gallon Cans to BuyRounded up.
- 2
- Paintable Area
- 292.0 sq ft
- Paint Needed in Litres
- 6.3 L
Step by step
- 1Values used
- 2Room Paint Needed
- 3Paint Needed= 1.67 gal
- 41-Gallon Cans to Buy= 2
- 5Paintable Area= 292.0 sq ft
- 6Paint Needed in Litres= 6.3 L
Assumptions and limits
- The result is derived only from the 7 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Room Paint Needed calculated?
Wall area = 2 x (length + width) x height, plus the ceiling if painted, less 20 sq ft per opening; paint = area x coats / spread rate Paint is sold by volume but used by area, so the calculation runs area first. The walls of a rectangular room are the perimeter - twice the length plus the width - multiplied by the ceiling height, which is why a long thin room takes more paint than a square one of the same floor area. Doors and windows come off at roughly 20 square feet each, and the ceiling goes on only if you are painting it. Divide the result by the spread rate on the can and multiply by the number of coats. Two coats is the normal answer rather than a luxury: one coat of most colours over a different base leaves a patchy, translucent finish. Buy in whole cans and expect the last one to be part-used - it is worth keeping for touch-ups, since a later batch will not match exactly.
Why does Room Paint Needed matter?
Under-buying is the expensive mistake, because a second trip usually means a different batch and a visible seam where the two meet.
What values do I need to enter?
This calculator takes 7 inputs: Room length, Room width, Ceiling height, Coats, Doors and windows, Spread rate, Painting the ceiling too. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.