Working out how much paint you need is a two-minute sum if you know three things: the real square metres of wall, the real coverage of the product and how many coats you're going to apply. The usual mistake is to trust the coverage on the label without adjusting it for the surface, and end up with a half-used tin or going back to the shop with the second coat half done. Here's the method, a table by room and the coverage of our products.
The formula
Litres needed = (square metres × number of coats) ÷ coverage per coat (m²/L).
For MATE5000 the manufacturer gives a coverage of 5–7 m²/L per coat, depending on how much the wall absorbs. Calculating with 6 m²/L and two coats, the sum comes down to: square metres ÷ 3 = litres. With the real coverage of 5–7 m²/L, a 4 L tin does around 10–14 m² with two coats and a 15 L tin around 37–52 m².
For Pared Seca the data sheet gives 10–12 m²/L per coat, around 6 m²/L with the two recommended coats: the 2 L DoyPack does around 12 m² with two coats.
Step 1: measure the square metres
- Measure the perimeter of the room (the sum of the four sides) and the ceiling height. Multiply them. That's the total wall area.
- Take off the openings: a standard door is 1,6 m², an ordinary window 1,5 m², a large picture window 3–4 m². Only take off the large openings; sockets and small details don't count.
- If you're painting the ceiling, add the length × width of the room.
- If you're only painting one wall, measure that one: width × height, minus openings.
Example: a 3 × 4 m bedroom with a 2,5 m ceiling. Perimeter 14 m × 2,5 = 35 m². Take off the door and window: 35 − 3,1 = 31,9 m². Round up to 32 m². With the ceiling: 32 + 12 = 44 m².
MATE5000 AntiHumedad
Breathable, anti-condensation interior paint with a deep matt finish.4 L and 15 L · 12 colours · 5–7 m²/L
Step 2: adjust for the surface
The coverage on any label is measured on a smooth, previously painted surface. Other surfaces use more:
| Surface | Extra consumption | Why |
|---|---|---|
| Smooth, previously painted wall | 0 % | It's the benchmark |
| Wall repaired with filler or new mortar | +10–15 % | Repairs absorb more on the first coat |
| Textured (gotelé) finish or rough render | +30–40 % | More real surface per square metre |
| Unplastered block or brick | +50 % or more | Very absorbent and full of gaps |
| Changing from a dark colour to a light one | Possible third coat | Hiding power |
Always add a 10 % margin for touch-ups and cutting in. It's cheaper to have half a litre left over than to run short halfway across a wall: the second purchase never arrives in time and the join between areas shows.
Step 3: how many coats
Two. A single coat doesn't cover well or give the thickness a breathable, anti-condensation paint needs; the technical data sheet says 2 or 3 coats. Three coats only when you're changing from a dark colour to a light one, when the surface is very uneven or when the first coat has been absorbed unevenly after a large repair. If you're unsure about the colour, remember that on screen it may differ from the real thing.
Table by room with MATE5000
Ceilings at 2,5 m, openings already deducted, smooth surface, two coats. Add the margin for the surface if your case calls for it.
| Room | Walls (m²) | Litres for walls | Tins | With ceiling (m²) | Tins with ceiling |
|---|---|---|---|---|---|
| One 4 × 2,5 m wall | 10 | 3,3 | 1 × 4 L | — | — |
| Bathroom 2 × 2 m (tiled to half height) | 9 | 3,0 | 1 × 4 L | 13 | 2 × 4 L |
| Kitchen 3 × 3 m (tiled to half height) | 14 | 4,7 | 2 × 4 L | 23 | 2 × 4 L |
| Bedroom 3 × 3 m | 27 | 9,0 | 3 × 4 L | 36 | 3 × 4 L |
| Bedroom 3 × 4 m | 32 | 10,7 | 3 × 4 L | 44 | 1 × 15 L |
| Living room 4 × 5 m | 41 | 13,7 | 1 × 15 L | 61 | 1 × 15 L + 2 × 4 L |
| Hallway 1,2 × 6 m | 30 | 10,0 | 3 × 4 L | 37 | 1 × 15 L |
Once you go over about 13 L, the 15 L tin is worth it: it works out cheaper per litre than four 4 L tins. If the wall has repairs or a textured (gotelé) finish, allow 15–25 % more. Whatever is left over will do for touch-ups a year from now, which is when a wall with a history of damp is worth checking.
A 4 L tin costs 19,02 € and a 15 L tin 65,79 €. A 3 × 4 m bedroom including the ceiling takes one 15 L tin. On the MATE5000 product page you enter your square metres and the calculator puts together the cheapest order that covers them.
How much primer or sealer you need
The preparatory treatments aren't applied to the whole wall, only to the affected area plus a margin, so consumption is much lower:
- NeutralySalt Primer (salts and rising damp): 1 L covers 25–30 m². A band of salts 1 m high along an 8 m wall is 8 m². For that band around 0,3 L per coat is enough: the 1 L container is more than enough, and the 5 L one does a whole ground floor or a garage.
- Sellador Total L44 (primer before painting): 9–10 m²/L per coat. It's used on new, absorbent or weak surfaces, or ones with a history of algae, mould or fungi, once the water getting in has been stopped. For a small area the 750 ml container is enough; for a whole 10 m² wall, a little over a litre per coat: the 4 L one.
- Cool Roof Therm (roofs): it's applied to the whole flat roof, so here you do measure the full surface. The data sheet gives an approximate coverage per container (4 L ≈ 10 m², 15 L ≈ 40 m²) and says to apply several coats until you reach 1–1,5 kg/m² in total. To avoid running short, calculate with that load: around 0,83–1,25 L/m². We explain it with examples in how to waterproof a flat roof.
If you have several types of damp in the same home, the kit bundles Sellador Total L44 with the paint so you don't buy more than you need.
Common calculation mistakes
- Counting the floor area instead of the wall area. A bedroom with 12 m² of floor has more than 30 m² of wall.
- Forgetting that it's two coats. If the product gives its coverage per coat, you have to double it.
- Buying the exact amount. The 10 % margin isn't optional on repaired walls.
- Using what's left in a tin of another brand "for the first coat". If it's an ordinary emulsion paint, you've just cancelled out the breathability of the paint you put on top.
- Calculating the primer for the whole wall. It only goes on the affected area and its margin.
If you manage several homes
For homeowners' associations, property managers or renovation companies treating several flats at the same time, it makes more sense to calculate by total square metres and order in volume. Write to us with the total square metres and we'll put the order together for you. And if you're not sure which preparatory treatment each wall needs, first look at how to tell what kind of damp you have in 5 minutes or let the photo diagnosis tell you before you order anything.
Guía escrita y revisada por el Equipo Humix Paint con los datos de las fichas técnicas de cada producto. La pintura actúa en la superficie: si el agua sube del suelo o entra de fuera, primero se trata la causa.
