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Paint calculator - Calcureno
Not sure how much paint your project needs?
Calcureno estimates the area to paint (m²) and the litres your walls need — so you buy less waste.
Ordering the right amount means fewer unused cans and less waste.
Live result
Area to paint
31,5m²
Paint needed
6,3L
for 2 coat(s)
You need about 6,3 L of paint
Suggested cans
1 pot de 5L + 3 pots de 0,5L
Total 6,5 L (~0,2 L spare)
Show calculation breakdown
- Floor perimeter
- 14 m
- Gross wall area
- 35 m²
- Doors deducted
- −2,5 m²
- Windows deducted
- −1 m²
- Bay windows deducted
- −0 m²
- Net area
- 31,5 m²
- Coats / coverage
- 2 · 10 m²/L
- Litres calculated
- 6,3 L
How the calculation works (and why)
We measure the vertical strip that runs around the room. Twice (length + width), times ceiling height: that is the gross area of the four walls, in m², shown first in the result.
Then openings come off. Defaults: door 2.5 m², window 1 m², bay window 4 m² — typical sizes. Front door or oversized bay? Edit the fields in the tool.
Area = 2 × (L + W) × H − doors − windows − bays
Litres = (Area × coats) ÷ coverage
Coverage (m² per litre) depends on paint type and how thirsty the substrate is. Calcureno uses manufacturer averages for a smooth wall. On render or very absorbent plaster, go generous — render soaks up far more than a wall that already has paint on it.
Average coverage by paint type
There is no single official standard. Each brand publishes a figure on the datasheet, measured in the lab on a smooth substrate. The ranges below are the ones you see most often; “In the tool” is the value Calcureno uses.
| Type | Typical range | In the tool | Notes |
|---|---|---|---|
| Interior matt paint | 9–11 m²/L | 10 m²/L | Hides flaws better. Uses a bit more per m². |
| Interior satin paint | 11–13 m²/L | 12 m²/L | Tighter film. In practice often slightly more economical per litre. |
| Exterior facade paint | 6–9 m²/L | 8 m²/L | Render, brick, cement: porous or textured → lower coverage. |
- Interior matt paint: Technical datasheets Dulux Valentine / Seigneurie (matt acrylic ranges)
- Interior satin paint: Technical datasheets Tollens / Ripolin wall satin
- Exterior facade paint: Facade manufacturer guides (e.g. Zolpan, Seigneurie Facade)
Frequently asked questions
Do I really need two coats?
Yes in most jobs. Colour change, new plasterboard, or a porous wall: one coat often leaves an uneven film. Manufacturers quote finish coverage for two coats anyway. So the tool defaults to 2. A same-colour matt touch-up on a sound wall can work in one coat — that is the exception.
How do I work out a ceiling?
This tool is walls only (perimeter × height). Ceiling: length × width, × coats, ÷ coverage. No door or window deductions. Do not relabel the wall result as a ceiling figure.
Is out-of-date paint still usable?
The date on the tin is a best-before, not a food expiry. Sealed acrylic, kept frost-free and out of strong heat, often lasts 1–2 years after opening if it has not coagulated, gone mouldy, or separated for good. Stir hard. Persistent lumps or a rotten smell → dispose of it. Do not thin a doubtful tin to “save” it.
Should primer litres be in this total?
No. The tool estimates finish paint. Primer has its own coverage, often around 10–12 m²/L, usually one coat. New plasterboard or a sharp colour jump: budget a primer tin on top of the displayed result.
Why does my tin show a different coverage?
The label beats our average. A premium one-coat product may claim 12–14 m²/L; a textured facade paint can drop under 6 m²/L. To match what you bought, use the tin’s figure instead of the tool’s.
What about heavily textured walls or render?
Real painted area exceeds flat geometry. Go generous — render soaks a lot. In practice +15 to +25 % product, or drop coverage (e.g. 10 → 8 m²/L).
Common mistakes when estimating paint
Skipping primer on new substrates
Fresh plasterboard or new render: the finish sinks in. Patchy look, real use well above the label figure. A suitable primer locks absorption before the topcoat.
Using smooth-wall coverage on a textured wall
Render, coarse glass fibre, painted brick — developed surface area jumps. Sticking with 10 m²/L here clearly underestimates what you need.
Ignoring cutting-in and corners
Geometry ignores brush losses. Corners, skirting, window edges: on a DIY job, add roughly 5–10 % above the suggested tin mix.
Mixing different batches of the same colour
Same product code, different batch numbers: shade can drift slightly. For a visible room, buy enough from one batch. Otherwise tip every tin into one bucket first (boxing).
Folding floor or ceiling into this calculator
The tool only handles vertical walls. Ceiling: length × width, with its own coverage — usually a dedicated ceiling paint.