Paint Calculator UK · metric

Litres of paint and primer for walls and ceilings, by area and coats. Metric units and £ costs, updated for 2026.

Last reviewed July 2026 · Free · Nothing you enter is stored

How this calculator works

Emulsion covers roughly 12 m² per litre per coat, so litres = area × coats ÷ 12, rounded up to whole tins. Primer/undercoat covers about 10 m² per litre. Coverage varies by surface and colour — always check the tin.

The waste allowance

This calculator rounds up to whole tins, because paint is sold in 2.5 litre and 5 litre units and not by the litre you actually need. It does not add a blanket percentage on top. The real variability in paint is not spillage, it is coverage: a published spread rate in square metres per litre assumes a particular film thickness on a surface that is already sealed, and a surface that drinks material uses more of it before the film reaches that thickness. The honest allowance is therefore a judgement about the wall rather than a fixed number. On new plaster, filled repairs, bare timber, MDF or render, expect the figure on the tin to overstate what you will get, and buy on the generous side. A spare half-tin in the cupboard is worth having anyway, because touching in a scuff two years later with a fresh tin of the same colour rarely goes unnoticed.

What “up to 17 m² per litre” actually means

The figures British manufacturers print are real and they are published. Crown Trade Vinyl Matt states up to 17 m² per litre, which works out at up to 85 m² from a 5 litre tin. Dulux Trade Vinyl Matt is quoted at up to 17 m² per litre on average. Dulux Trade Supermatt, which is a different product for a different job, is quoted at 18 m² per litre. Retail Dulux Matt, the tin most people actually pick up in a DIY shed, is quoted lower at up to 14 m² per litre.

Two words in those claims carry most of the weight, and they are “up to”. Coverage is not a property of the paint on its own. It is the relationship between a volume of material and the thickness of the film that volume is spread into, on a surface of a particular porosity and texture. Spread thin over smooth sealed plaster, a litre covers a large area badly. Spread at the thickness the manufacturer tested, it covers the stated area and behaves the way the data sheet says it will.

That is why this calculator plans on roughly 12 m² per litre per coat for emulsion rather than 17, and it is worth saying so plainly rather than quietly. The lower figure is a planning allowance, not a published one. It exists because most walls in most British houses are not the smooth sealed test panel the higher number was measured on, and because running out of a mixed colour halfway through a wall costs more than a spare tin does. If your walls are sound, previously painted and genuinely smooth, you will beat 12 comfortably and have paint left over. That is the intended failure mode.

New plaster, the mist coat, and why fresh work drinks paint

Bare plaster is the single biggest reason a British paint order goes wrong, and it is not really a coverage problem. Fresh plaster is porous and alkaline. Neat emulsion applied straight onto it forms a skin on the surface while the water underneath is pulled into the plaster, and the result is a film that has not keyed properly and can peel away in sheets, sometimes taking a strip the size of a hand with it.

The standard remedy is a mist coat: a first coat of emulsion thinned with clean water so that it soaks in and seals rather than sitting on top. The manufacturers publish their own ratios and they differ. Dulux Trade Supermatt is specified with a first coat thinned at up to one part clean water to three parts paint, followed by two coats thinned to roughly one part water to five. Crown Trade Covermatt is specified with a mist coat diluted with 40 per cent clean water by volume. Use the ratio for the product in your hand rather than a general rule of thumb.

For the arithmetic, the practical consequence is that new plaster needs three coats rather than two, and the first of them is thinned, so it goes further per litre than the ones that follow. Filled and patched areas behave the same way in miniature. Filler is more absorbent than the paint around it, and a wall that has been made good in a dozen places will flash and show every repair through a single finish coat, which is a coverage problem dressed up as a colour problem.

Colour, obliteration, and why two coats is the standard

Hide is a property of pigment, not of price or effort. Bright and transparent pigments hide poorly by their nature. Yellows, oranges, reds and clean primaries are the usual offenders, and they often need two coats or more whatever is underneath, because the pigment itself does not block what is behind it. Muted and greyed shades hide better, because the pigments that produce them are more opaque. That is chemistry rather than quality control, and it applies to a fifty pound tin as much as a fifteen pound one.

British trade data sheets acknowledge this directly. Crown Trade Covermatt, an obliterating emulsion quoted at up to 16 m² per litre on smooth surfaces, instructs two coats as required and adds that certain colours may need additional coats to give complete obliteration. Crown Trade Vinyl Matt says much the same, specifying two full coats with strong colour changes possibly needing more. Neither publishes a table telling you which colours, because the answer depends on the shade you have chosen and the shade you are covering.

Two coats is the standard for durability as well as for hide. A single coat, even one that reads as solid from across the room, is a thinner and less continuous film. It burnishes sooner where it is touched and it does not scrub as well, because there is simply less material there to scrub. Sheen shows this before colour does, which is why a one-coat job in soft sheen or silk looks patchy in raking light even when the colour looks even. Buy for two coats and treat a third as the contingency rather than the plan.

Tins come in 2.5 and 5 litres, and that is what you are really buying

Paint is sold in fixed units, so the litre figure this calculator returns is an input to a purchasing decision rather than the decision itself. The common domestic sizes are 2.5 litres and 5 litres, with trade ranges extending upward. Dulux Matt, for instance, lists 2.5 L, 3 L, 5 L, 6 L, 7 L, 7.5 L and 10 L tins, so the sizes available depend on the exact product and finish as much as on the brand.

The awkward case is the order that lands just above a tin boundary. Needing 5.4 litres means buying 7.5 litres in practice, and that is worth knowing before you commit to a colour, because it changes the real cost of the job by more than the difference in price per litre between a trade and a premium range. Where a job sits just over a boundary, it is often cheaper to buy the larger tin than a 5 litre plus a 2.5 litre, and it is always better than two trips.

One more practical point about buying in one go. Mixed colours are tinted to order from a base, and while modern tinting machines are consistent, two tins mixed weeks apart are not guaranteed to be identical. If the job needs more than one tin, buy them together, and if you are working across a large uninterrupted wall, box them: pour the tins into a single larger container and stir, so that any small difference is spread across the whole wall rather than showing as a line where one tin ran out.

Published coverage figures from British manufacturers

These are the figures the manufacturers themselves state, in square metres per litre. Every one of them is a best case on a smooth, sound, sealed surface. They are listed here so you can see the spread between products, not so you can plan a job at the top of the range.

Coverage figures as stated by the manufacturers and their retailers: Crown Trade Vinyl Matt (Toolstation product data, up to 17 m² per litre, up to 85 m² per 5 L tin); Dulux Trade Vinyl Matt (B&Q product data, up to 17 m² per litre on average); Dulux Trade Supermatt (The Paint Shed product data, 18 m² per litre, mist coat thinned up to 1 part water to 3 parts paint); Crown Trade Covermatt technical data sheet (up to 16 m² per litre on smooth surfaces, mist coat diluted 40 per cent by volume); Dulux Matt at dulux.co.uk (up to 14 m² per litre). The 12 m² per litre planning figure is this site's own allowance and is not published by any manufacturer.

What goes wrong when buying paint

Planning at the top of the range. Up to 17 m² per litre is a best case on smooth sealed plaster. New plaster, filler, bare timber and render all absorb material before a film forms, so the real figure comes in lower and the shortfall is discovered halfway up a wall.

Putting neat emulsion on new plaster. Fresh plaster pulls the water out of an unthinned coat and the film never keys properly. It can peel away in sheets. Thin the first coat as the manufacturer specifies — 40 per cent water for Crown Trade Covermatt, up to 1 part water to 3 parts paint for Dulux Trade Supermatt.

Buying for one coat. Two coats is the specified standard for durability as much as for hide. A single film is thinner, less even and does not scrub as well. Crown's own data sheet allows for strong colour changes needing more than two.

Expecting a bright colour to behave like a muted one. Yellows, oranges, reds and clean primaries hide poorly because of the pigments involved. Crown Trade Covermatt's data sheet says outright that certain colours may need additional coats for complete obliteration. That is inherent to the colour, not a fault in the tin.

Buying tins piecemeal. Mixed colours are tinted to order and tins mixed weeks apart are not guaranteed identical. Buy the whole job in one go, and box multiple tins together before starting a large wall.

Frequently asked questions