Paint Calculator
Paint is worked out from wall area, not floor area: measure the perimeter, multiply by the ceiling height, take off the doors and windows, multiply by the number of coats, and divide by the coverage printed on the tin. This does that, then rounds up to whole tins — because you cannot buy 0.7 of a tin, and the rounding is usually where an estimate goes wrong.
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Paint needed
7.71 L
Total paint cost
$120.00
Details
Updates as you typeFloor measurement of the longer wall. This paints walls, not the ceiling or floor.
Floor to ceiling. 2.4 m (8 ft) is the usual modern ceiling height.
Each door removes 20 sq ft (1.86 m²) of wall from the total.
Each window removes 15 sq ft (1.39 m²) of wall from the total.
Two is standard. Allow three over a strong colour or bare plaster.
Printed on the tin. Emulsion is typically 10-13 m² per litre, or 400-500 sq ft per gallon.
The size you actually buy — 2.5 L and 5 L tins in metric shops, quarts and gallons in US ones.
What one tin of the size above costs.
Summary
A useful touch-up amount — 10% to 25%Paint needed
7.71 L
Paint purchased
10.00 L
- Goes on the wall7.71 L77%
- Left over2.29 L23%
- Tins to buy
- 4 tins
- Total paint cost
- $120.00
- Wall area to paint
- 38.6 m²
- Area over all coats
- 77.1 m²
- Paint purchased
- 10.00 L
- Paint left over
- 2.29 L
- Tins are rounded up, never averaged: a job needing 3.1 tins takes 4. That is why the cost jumps in steps as the room grows, and why a slightly larger tin size sometimes costs less overall.
- Walls only. Ceilings, skirting, architrave and doors themselves are separate jobs with their own coverage, and ceiling paint is usually a different product.
- Coverage on the tin is measured on smooth, sealed, primed wall. Bare plaster, textured or heavily patched surfaces drink noticeably more, so treat the tin figure as the best case.
How this is calculated
- Wall perimeter = 2 × (length + width)
- 18.00 m
- Gross wall area = perimeter × height
- 43.20 m²
- Doors (1 × 1.86 m²)
- 1.86 m²
- Windows (2 × 1.39 m²)
- 2.79 m²
- Net wall area = gross − openings
- 38.55 m²
- Coats
- 2 coats
- Area to cover = net × coats
- 77.11 m²
- Coverage
- 10.00 m²/L
- Paint needed = area ÷ coverage
- 7.711 L
- Tin size
- 2.50 L
- Tins needed exactly = paint ÷ tin size
- 3.084 tins
- Tins to buy = rounded UP to a whole tin
- 4 tins
- Paint purchased = tins × tin size
- 10.00 L
- Left in the tin
- 2.29 L
- Price per tin
- $30.00
- Total cost = tins × price
- $120.00
Coats
Compare scenarios
See how one change moves the result
- CurrentYour inputs as they stand7.71 LCurrent
- Room lengthm 6.38.96 L
- Room widthm 58.67 L
- Wall heightm 39.87 L
Frequently asked questions
Why round up to whole tins?
Because shops sell tins, not litres. If the maths says 3.08 tins you buy 4, and you pay for all four — the 0.92 of a tin you did not need is real money on the receipt. Rounding to the nearest tin instead would leave a job 0.4 of a tin short, which means a second trip, and a second batch that may not match the first.
Should I deduct doors and windows?
Yes, once there is more than one or two. The standard allowances are 20 square feet (1.86 m²) per door and 15 square feet (1.39 m²) per window, which is what this uses. A room with one door and two windows loses about 4.6 m² — roughly a tenth of a typical wall area, so it is the difference between three tins and four.
How many coats do I actually need?
Two coats over a similar colour on a previously painted, sound wall. Three when you are going light over dark, covering a strong colour such as red or navy, or painting bare plaster and new plasterboard — and on bare surfaces the first coat should really be a primer or a mist coat, which has its own coverage figure.
What coverage figure should I enter?
The one on the tin, but treat it as the best case. Manufacturers measure on smooth, sealed, primed wall. Typical emulsion is quoted at 10-13 m² per litre (400-500 sq ft per US gallon); textured, porous or freshly filled surfaces can drop that by a third, and a roller with a deep pile lays paint on more thickly than the test does.
Does this include the ceiling?
No — it covers the four walls only. Ceilings are usually a different product, and their area is simply the room length times the width, which you can put through this calculator on its own by entering the ceiling as a separate job. Skirting, architrave and doors are trim paint, sold and covered differently again.
Is it cheaper to buy one big tin or several small ones?
Usually the big tin, per litre — but not always once rounding is counted. A job needing 7.7 litres takes four 2.5 L tins (10 L) or two 5 L tins (10 L), the same volume; a job needing 5.2 litres takes three 2.5 L tins (7.5 L) but two 5 L tins (10 L). The leftover percentage shown here is the number to compare.