Paint Calculator
Calculate how many litres of paint you need from the wall area, number of coats and coverage.
Formula last reviewed 4 August 2026 · How we verify our calculators
Paint required
16.7 L
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Frequently asked questions
Multiply the area by the number of coats and divide by the paint’s coverage per litre. 1,000 sq ft at two coats with 120 sq ft/L coverage needs about 16.7 litres.
Coverage varies by paint type and surface — typically 100–140 sq ft per litre. Use the figure on your paint can; rough or porous surfaces consume more.
Two coats is standard for good, even colour. A drastic colour change or a fresh, porous surface may need a primer plus two coats.
For a quick estimate you can use the gross wall area; subtracting large openings gives a tighter figure. Always keep a little extra for touch-ups.
Sixteen point seven litres for two coats
Painting 1,000 sq ft with 2 coats at a coverage of 120 sq ft per litre needs about 16.7 litres.
Paint = (area × coats) ÷ coverage per litre = (1,000 × 2) ÷ 120 = 16.67 L
The arithmetic is trivial. Everything that makes paint estimates go wrong sits in the two inputs: what the real area is, and what coverage the surface actually delivers.
Getting the area right
The wall area of a room is its perimeter times its height, not its floor area:
Wall area = 2 × (length + width) × height
A 12 × 15 ft room with 10 ft ceilings has 2 × 27 × 10 = 540 sq ft of wall, against 180 sq ft of floor. Estimating from floor area understates by a factor of three.
Deduct openings: a standard door is about 20 sq ft, a window 12–15 sq ft. For a room with one door and two windows, that is roughly 50 sq ft off.
Add the ceiling separately if painting it — that is the floor area.
Coverage, and why the tin is optimistic
Manufacturers quote coverage on a smooth, sealed, previously painted surface. Real surfaces vary widely:
- Smooth putty-finished interior wall, repaint — 120–140 sq ft/L
- Fresh plaster, first coat — 80–100 sq ft/L, because bare plaster absorbs heavily
- Textured or rough surfaces — 60–90 sq ft/L
- Exterior emulsion on rendered walls — 70–100 sq ft/L
A primer on new plaster is not optional if you want the quoted coverage on the topcoats — it seals the surface so the finish paint sits on it rather than soaking in. Skipping primer typically costs more in extra topcoat than the primer would have.
Dark over light, or a strong colour, frequently needs three coats rather than two. Reds and deep yellows are notoriously poor at covering.
Types, and where each belongs
Distemper — cheapest, chalky finish, not washable. Rarely worth it now except for temporary or low-use spaces.
Emulsion (acrylic) — the standard interior choice, washable, available in matt, satin and sheen. Low-VOC options are widely available.
Enamel — oil-based, hard and glossy, for wood and metal. Slow-drying with strong odour.
Exterior emulsion — formulated for UV and rain resistance, with elastomeric options that bridge hairline cracks.
Reading the result
The figure is for paint only. A complete job also needs primer (roughly one coat at similar coverage), putty for levelling on new or damaged walls, sandpaper, masking tape and sheeting.
Buy in standard tin sizes — 1 L, 4 L, 10 L, 20 L — and round up. 16.7 L means a 20 L tin, or a 10 L plus a 4 L plus a 4 L depending on price breaks. Larger tins are usually cheaper per litre.
Keep the leftover, sealed and labelled with the room. Touch-ups matched from a fresh tin rarely blend exactly, since batches vary slightly and paint on the wall fades.
Common mistakes
Estimating from floor area. Wall area is typically three times larger.
Trusting quoted coverage on new plaster. It absorbs far more.
Skipping primer. It costs more in topcoat than it saves.
Assuming two coats for a strong colour. Deep shades often need three.
Not deducting large openings. On a small room with big windows this matters.