Paint Coverage Calculator

Painting Guide

What do I need to know about Paint Coverage Rates?

Paint coverage varies by type, surface, and how heavily you apply it, and the rates on the tin are best-case figures for a well-prepared smooth surface. Standard emulsion (matt, silk, or eggshell wall paint) typically covers 12–15 m² per litre on a smooth, sealed wall. Gloss and eggshell on woodwork cover about 12 m² per litre. Specialist paints vary widely — masonry paint, anti-mould bathroom paints, and metal paints can cover anywhere from 6–14 m² per litre, so always read the tin rather than assuming. Coverage drops noticeably on porous, textured, or unprepared surfaces: bare plaster, raw wood, or rough render can absorb so much paint that the first coat covers as little as 6–8 m² per litre. New plaster needs a mist coat (paint thinned with water) which uses extra paint. Textured surfaces (artex, popcorn ceilings, rough brick) need much more paint than smooth — sometimes double — because the paint has to coat every undulation. A worked example: painting a 30 m² wall in emulsion at 14 m² per litre needs about 2.15 litres for one coat, or 4.3 litres for two coats — so a 5 litre tin covers it with a small reserve, but a 2.5 litre tin would run out partway through the second coat. This calculator applies a sensible coverage rate and waste allowance, but always cross-check against the specific tin you're buying.

How Many Coats?

The number of coats you need depends on the colour change and the surface, and getting it right is the difference between a professional finish and an obvious DIY job. As a general guide: painting light over light (or the same colour again) usually needs 1–2 coats. Painting dark over light needs 2–3 coats — the dark colour needs enough pigment to be properly opaque, and skimping leaves a streaky, uneven look. Painting white over dark is the hardest case and often needs 3+ coats of plain white; the smart approach is to use a tinted primer first (often grey, lighter than the dark colour you're covering), which dramatically reduces the number of topcoats needed because the primer evens out the underlying colour before you start with the final paint. Bright colours (strong reds, yellows) often need extra coats regardless of what's underneath, because their pigments are less opaque — many manufacturers warn about this on the tin. Primer matters: on bare plaster, wood, or any patchy surface, a coat of primer gives a uniform base that drinks up evenly and lets your topcoats cover predictably; skipping primer is the most common reason DIY paint jobs look uneven, especially in raking light. Don't try to make one heavy coat do the job of two thinner coats — heavy paint runs, drips, and dries unevenly, while two thin coats give a smoother and more consistent finish. Allow proper drying time between coats (check the tin; usually 2–4 hours for emulsion, longer for gloss in cool or humid conditions).

What's the key thing to understand about Buying Tip?

Two practical buying habits prevent the most common paint-shopping headaches. First, buy all the paint you need in one go, all from the same batch (the lot number is printed on every tin). Slight colour variations between batches are common — the same shade made on different production runs can differ subtly, and the difference becomes very visible if half a wall is painted from one batch and half from another. The best fix is having all your tins from the same batch from the start. Second, always round up rather than down when you're close to a tin boundary: if you've calculated you need 5.1 litres, buy a 5L tin plus a 2.5L tin (not just the 5L), because running out 0.5 litres short on the second coat with no time to get to the shop is a familiar disaster. Buying slightly too much is normal — keep the leftover tin labelled and sealed for touch-ups (a fresh-paint dab covers scuffs and scrapes for years), and most modern emulsion stores well for 2+ years in a cool dry place. Other practical tips: take a sample of the existing colour to the shop if you're trying to match (digital colour matching is widely available); test a small patch with a tester pot before committing to a colour, especially as colours look very different in your light versus the shop's; and consider buying primer separately rather than relying on one-coat 'self-priming' paints, which generally don't live up to the claim on difficult surfaces. This calculator's waste allowance assumes good practice; if you're going to skip primer or work on a textured surface, plan for more.

What do I need to know about Choosing the Right Paint?

Paint finish selection matters as much as colour. Matt finish hides surface imperfections but is not washable — suitable for low-traffic adult bedrooms. Eggshell and washable matt offers close-to-matt appearance with wipe-clean durability, suitable for most living spaces. Silk: higher sheen, highly washable but shows every surface imperfection — for kitchens and bathrooms. The difference between budget and premium paint is primarily pigment density: premium paints typically cover fully in 2 coats versus 3 or more for budget paint, often making them cheaper overall despite the higher price per tin.

What do I need to know about Coverage Rates for Different Surfaces and Paints?

Manufacturer-quoted coverage figures (often '12-14 m² per litre' on the tin) assume a smooth, properly prepared surface — rough, porous or textured surfaces soak up significantly more paint per square metre, which is the single biggest reason people run out of paint mid-job despite following the tin's figures.

These are typical ranges rather than guarantees — application method matters too, since spraying generally achieves closer to the manufacturer's quoted figure than rolling, and rolling achieves a more even film than brushing, which tends to apply paint less efficiently and leave more in the tray and roller sleeve unused.

What do I need to know about a Worked Example — Paint Needed for a Room?

Worked example: a bedroom measuring 4 m × 5 m with a 2.4 m ceiling height needs two coats of emulsion. The room has two doors (2 m² each) and one window (1.5 m²) that don't need paint, and the chosen emulsion covers a typical 12 m² per litre per coat on this smooth, previously painted plaster. Step 1 — wall perimeter: 2 × (4 + 5) = 18 m Step 2 — gross wall area: 18 m × 2.4 m = 43.2 m² Step 3 — deduct openings: 2 × 2 m² + 1 × 1.5 m² = 5.5 m² Step 4 — net paintable area: 43.2 − 5.5 = 37.7 m² Step 5 — paint needed per coat: 37.7 ÷ 12 = 3.14 litres Step 6 — paint needed for 2 coats: 3.14 × 2 = 6.28 litres Rounding up to available tin sizes, that's comfortably covered by a 5-litre tin plus a 2.5-litre tin (7.5 litres total), rather than just a single 5-litre tin, which would fall about 1.3 litres short of the full two-coat job. It's a useful habit to always round coverage calculations up to the next full tin size rather than down — running short mid-coat means mixing a slightly different batch to finish, which can show up as a faint tonal difference once the wall dries. New plaster complicates this further: a mist coat (diluted first coat, typically 70% paint to 30% water) spreads much further than a full-strength coat but still needs at least one full-strength coat afterwards, so budgeting for new plaster should use the lower, more porous coverage figures above rather than the smooth-plaster rate. Colour also plays a role that's easy to overlook: covering a dark existing wall colour with a much lighter new colour (or vice versa) often needs an extra coat beyond the two assumed in the worked example above, regardless of what the tin's coverage figure says, because the issue is contrast and opacity rather than the paint's raw spreading rate — which is why many manufacturers now sell dedicated high-opacity 'one-coat' formulations specifically aimed at big colour changes.