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Paint calculator: litres and tins for a room

Litres = m² to paint × coats × 0.1 l per m². Wall area is the room’s perimeter times its height, minus 1.64 m² per door and 1.56 m² per window; the ceiling adds length times width. With two coats that’s 0.2 l per m². Primer goes over the same area.

Are you painting the ceiling too?
Tins you’re going to buy

What you need

Area: 31.8 m²

MaterialQuantityUnit
Paint1 tin of 15 l6.36l
Primer (sealer)3.82l
Masking tape28m
Protective plastic sheeting17m²
  • 2 coats by roller on walls.
  • Deducted from the walls: 1 door of 0.8×2.05 m and 1 window of 1.2×1.3 m.
  • These are quantities for buying materials, not prices: the price of the job is fixed by the professional.

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Where the figures come from

The calculator uses the same usage norms that are used to measure up a job before buying materials. These are guide quantities for a flat surface: the exact amount depends on the surface, the cuts and how the person fitting it works.

Usage norms used in this calculation
NormValueSource
Paint by roller, one coat0.1 l per m²Source: standard building practice
Primer (walls and ceiling)0.12 l per m²Source: standard building practice
Door: opening width0.8 mSource: 72.5 cm leaf with frame (UNE 56801); CTE DB-SUA (Spanish building code): clear width of at least 0.80 m
Door: opening height2.05 mSource: 203 cm leaf with frame (UNE 56801); CTE DB-SUA (Spanish building code): clear height of at least 2.00 m
Window: opening width1.2 mSource: typical 120 cm bedroom window, joinery catalogues
Window: opening height1.3 mSource: between the usual sizes of 120 and 150 cm, joinery catalogues

Price, service and other calculators

This calculator doesn’t give prices. Market ranges, with their sources, are in the blog guides.

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Questions and answers

What people ask before going out to buy materials. If your question isn’t here, message us on WhatsApp.

How much paint do you use per square metre?

The calculator counts 0.1 l per m² per coat, applied with a roller. With two coats that’s 0.2 l per m². A very porous wall, fresh plaster or a big change of colour uses more, so it’s best not to buy the bare minimum.

Do I need two coats?

Almost always. The first coat evens things out and the second gives the colour and an even finish. One coat is usually only enough when touching up in the same colour over a wall in good condition. The calculator assumes two coats by default and you can change it.

Are doors and windows deducted?

Yes. Each door takes off an opening of 0.8 × 2.05 m and each window one of 1.2 × 1.3 m, which are the usual sizes in Spanish homes. If you have a large picture window or a double door, count one extra window or door.

Should I buy 4-litre or 15-litre tins?

Choose the size you’re going to buy in the calculator and it tells you how many tins you need, rounding up. For a small room the small tin is usually enough; for a living room or several rooms in the same colour, the big one avoids differences in shade between tins.

Do I need primer?

On new plaster or plasterboard, on walls repaired with filler and when switching from plastic (vinyl) paint to a different base, yes. The calculator counts 0.12 l per m², one coat, over the same surface as the paint: walls and, if you tick it, the ceiling. On a wall that’s already painted and sound you can do without.