Calculator
Paint Calculator
Enter the room dimensions and get the net paintable area, the litres required and how many tins to buy. Doors and windows are deducted from the walls; the ceiling is optional.
Room dimensions
Area one litre covers in a single coat. For water-based interior paint the typical range is 8–14 m²/L; it is printed on the tin.
Result
- 7.5 L× 1 pcs
- 2.5 L× 1 pcs
The suggested tins never fall short of what you need; the surplus is kept for touch-ups.
Assumptions behind the calculation
- A standard internal door is taken as 1.9 m² and an average window as 1.6 m², both deducted from the wall area.
- If the ceiling is selected, width × length is added; no openings are deducted from the ceiling.
- The spreading rate can be replaced with the figure on your tin — covering a dark colour with a light one lowers the real rate.
- Primer is assumed at 9 m²/L and calculated as a single coat.
The three most common mistakes when buying paint
Getting the quantity right saves the working day rather than the money. Running out mid-job also creates a colour-matching problem.
Not deducting doors and windows
In an average room, openings take up 8–12% of the wall area. Skip the deduction and you buy more than you need — and leftover paint rarely matches on the next job.
Calculating a single coat
Two coats are standard indoors; one coat lets the previous colour shadow through. Covering a dark colour with a light one may need three. The coat count multiplies the litres directly.
Forgetting the primer
Fresh plaster, skim coat and repaired patches absorb paint. Without primer the first coat disappears and even the second fails to cover. Primer saves paint and evens out the colour.
NET AREA = PERIMETER × HEIGHT − (DOOR + WINDOW AREA) [+ CEILING]
LITRES = NET AREA × COATS ÷ SPREADING RATE (m²/L)
TINS = LITRES, split into 15 / 7.5 / 2.5 L containers
How many square metres does one litre of paint cover?
For water-based interior paint it is 8–14 m² in a single coat, with 11 m²/L as a fair average. The figure is printed on the tin and varies by brand. On absorbent surfaces — fresh plaster, skim coat, repaired areas — the real rate drops sharply, and primer largely closes that gap. Spraying uses more material than rolling for the same area.
How many coats of paint are needed?
Two coats are standard indoors. A single coat lets the underlying colour shadow through and leaves the surface patchy. Going from a dark colour to a light one needs three coats or an opaque primer. Refreshing the same colour can be done in one. Because the coat count multiplies the litres directly, it is the single most decisive input in the calculation.
Should doors and windows be deducted?
Yes. In an average room openings account for roughly 8–12% of the wall area, and ignoring them means buying too much. This tool assumes 1.9 m² for a standard internal door and 1.6 m² for an average window. If your openings differ substantially, it is more accurate to work out the net area yourself and enter it directly.
How much extra should be allowed for waste?
Because paint is sold in 2.5 / 7.5 / 15 litre tins, a small surplus is left over anyway and that is enough for touch-ups. No separate waste allowance is needed. Store the surplus tightly sealed: a touch-up from the same batch matches, while a newly bought tin of the same name often does not.
Can the ceiling be painted with the same paint as the walls?
Usually not. Ceilings take a matt, non-reflective product while walls take a washable one. Ticking the ceiling in this tool adds its area to the total, but if you are buying two different products it is more accurate to calculate walls and ceiling separately.
This tool gives an initial estimate and does not replace a site survey. Real consumption varies with surface absorbency, colour change, application method (roller, brush, spray) and the decorator's technique.
Shall we handle the painting?
You have the quantity; let us run the work as well. In Ankara we carry out painting, plastering and surface preparation with our own team, and quote after seeing the space.
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