Paint Coverage Explained: Walls, Floors, Fences & Masonry (2026 Guide)

Most paint is over-bought or runs out for the same reason: a coverage number guessed instead of calculated. This guide fixes that with one formula, typical coverage rates for every surface you are likely to paint — smooth and textured walls, new plaster, masonry, brick, concrete floors, rough-sawn and planed fencing — and a fully worked 4 × 5 m room example showing the arithmetic end to end. Dulux and Valspar typical per-litre figures are covered too, along with why exterior jobs legitimately need 10–20% more paint than the tin suggests.

The paint coverage formula

Multiply each wall's length by its height, subtract the doors and windows, then divide the result multiplied by your number of coats by the coverage rate on the tin. Written out: Litres = ((wall area − openings) × coats ÷ m² per litre) × 1.1 for wastage. Every section below applies that formula to a different surface.

Break every job into the same four steps. They take two minutes with a tape measure and a phone, and they are identical whether you are painting a bedroom, a garage floor or a fence line.

1. Measure and multiply. For each wall, work length × height. In a rectangular room you can shortcut with perimeter × height — for the worked example below that is 2 × (4 + 5) × 2.4 = 43.2 m² of gross wall. Ceilings are measured separately as flat area.
2. Subtract the openings. A standard internal door (0.9 × 2 m) is 1.8 m²; the window in our worked example (2 × 1.4 m) is 2.8 m². Skip anything under roughly 0.5 m² — radiator recesses and vents sit inside the wastage margin anyway.
3. Apply the coats. Litres = Area × number of coats ÷ coverage-rate. Two coats double the requirement; a diluted mist coat on fresh plaster counts as its own line, so a "two-coat" new-plaster job is really three passes.
4. Add 10% wastage. Roller nap holds paint, trays dry out, edges get over-brushed. Ten per cent is the standard interior allowance; 15–20% is normal outside or when spraying, for reasons the exterior section below details.

Written on one line: gross area − openings, × coats, ÷ m²-per-litre, × 1.1. The only variable that changes between surfaces is the coverage rate — which is exactly what the baseline figures pin down next.

Standard coverage: how far does one litre go?

As a rule of thumb, most emulsion and wall paints cover 10–13 m² per litre on smooth, primed surfaces — roughly 100–130 sq ft per litre. In US units, a gallon typically covers 350–400 sq ft on smooth walls. Rough, bare or porous surfaces can cut those figures nearly in half.

Three things decide where inside that range you land:

• The surface. Smooth, sealed, primed plaster delivers the full rate. Bare plaster, unsealed timber and sanded MDF drink a first coat before the film starts to build.
• The application. A long-nap roller holds back paint that a short-nap roller would deliver; sprayers lose mist to the air; worn brushes lay uneven films that force a heavier second pass.
• The colour change. White over deep navy is a three-coat job in practice — a tinted undercoat counts as one of the three and is cheaper than extra topcoats.

For quick mental maths, as a rule of thumb: m² × coats ÷ 12, then round up to the next tin size. In imperial units, think 100–130 sq ft per litre, or the familiar US figure of 350–400 sq ft per gallon on smooth walls. Treat the number on the tin as a laboratory result measured on a smooth primed board — your wall gets a vote, and the 10% wastage margin is how you pay for its opinion.

Coverage per surface type

Coverage is decided by the surface at least as much as by the paint. Smooth interior walls sit at the top of the range at 12–14 m² per litre; textured walls, bare masonry and rough-sawn timber drop to 6–9 m² per litre. Use the table below as your plug-in rate for the formula or any paint coverage calculator.

Two conventions keep this table honest. First, every rate is per coat — multiply by coats before dividing, or let the paint coverage calculator do it. Second, a mist coat on new plaster is a separate purchase of area: the diluted first coat typically manages only 6–10 m²/L, then your two full topcoats follow at the normal wall rate. A "two-coat" repaint of fresh plaster is therefore a three-pass job in the calculation.

Exterior vs interior: why outside needs 10–20% more

An exterior paint coverage calculator should always assume a lower coverage rate than the same paint achieves indoors. Weathered surfaces absorb more, wind carries spray mist away, textured render adds surface area, and sun makes paint tacky mid-roll. As a rule of thumb, add 10–20% on top of your interior calculation for the same measured area.

Four forces push coverage down outside, and each one has a practical fix:

• Absorption. Weathered timber, uncoated render and faded paint are porous. The first coat is partly a soaking-in exercise — on chalky surfaces a stabilising primer is cheaper than a wasted topcoat.
• Wind-spray wastage. Airless sprayers lose 10–20% of paint to drift outside, even on a calm day. Brush and roll what you can; if you must spray, screen the area with sheeting.
• Real surface area. Pebbledash, deep-textured render and rough-sawn cladding carry 15–25% more surface than their flat measurements suggest. Measure flat, then add.
• Heat and tack. Hot substrates flash-dry paint mid-roll, forcing heavier passes to keep a wet edge. Work in shade where you can.

Net effect: an exterior paint coverage calculator that runs on interior rates will under-quote every time. Take the litres you would need indoors and add 10% for sound, previously painted surfaces, or 20% for bare, weathered or strongly textured ones — then round up to the tin. On big masonry jobs, one 5 L tin above the calculation is cheaper than stopping halfway through a coat.

Floor paint coverage

Concrete and timber floors typically cover 8–10 m² per litre, but a floor paint coverage calculator should always run two coats as the minimum. Floors take abrasion that walls never see, and a single thin coat wears through within months. Drying is not curing: paint can be touch-dry in hours yet needs days to reach full hardness.

Floor projects punish optimistic maths more than any other surface:

• Two coats is the floor, not a luxury. Feet, castors and chair legs abrade constantly. Two thin coats cure harder than one thick one, and a thick coat stays soft longer.
• Bare concrete drinks the first coat. Unsealed slabs can pull an 8–10 m²/L coat down to 5–6 m²/L. If the first coat vanishes into the slab, treat it as your primer and the maths still holds.
• Drying ≠ curing. Touch-dry in a few hours; recoat within the window on the tin (often 4–24 hours); full chemical cure typically takes 5–7 days. Keep furniture and vehicle tyres off until cured, or you will print them into the film.
• Prep decides adhesion. Degrease, etch or mechanically abrade smooth power-floated concrete, and fill cracks first — paint laid over dust or oil lifts in sheets.

Worked quickly: a 6 × 4 m garage floor is 24 m². Two coats at a typical 9 m²/L comes to 24 × 2 ÷ 9 = 5.33 L, and 5.33 × 1.1 ≈ 5.9 L with wastage — round up to 6 L. One extra coat on bare, thirsty concrete is always cheaper than repainting scuffed patches next spring.

Masonry and brick paint coverage

Bare brick and masonry typically manage 6–9 m² per litre because the surface drinks paint. A masonry paint coverage calculator or brick paint calculator should use the low end for rough, porous stock and the high end for rendered or previously painted walls. A stabilising primer reduces suction and pushes real-world coverage back toward the tin figure.

Masonry is the thirstiest surface most painters meet, and it punishes shortcuts:

• Porosity rules everything. Bare brick, block and old render suck binder out of the first coat, leaving it thin and chalky. Two coats are standard; the first is partly filling suction.
• Stabilising primer is the multiplier. A diluted stabilising solution evens out absorption across the wall so the topcoat spreads at its normal rate instead of the worst patch's rate. On chalky or flaking masonry it is not optional.
• New render needs patience. Fresh render and concrete stay alkaline for weeks; paint too early and alkali attacks the binder. Most masonry paints ask for a cure period — commonly around four weeks — before coating.
• Count the texture. Deep texture adds 15–25% of real area. Measure the wall flat, then add 20% before you apply the rate.

Typical single-coat rates: 6–9 m²/L on bare brick and block, closer to 10 m²/L on sound, previously painted walls. A brick paint calculator set to the mid-range on bare porous stock will under-buy; use the low end and treat the stabilising primer as its own line in the litres.

Fence paint coverage: rough vs planed timber

Rough-sawn fence timber typically absorbs 6–8 m² per litre, while smooth planed panels manage 8–10 m² per litre. For a standard 1.8 × 1.8 m panel painted on both faces with two coats, that works out at roughly 1.9 litres for rough-sawn wood and 1.5 litres for planed boards — before any 10% wastage allowance.

The per-panel arithmetic is the clearest way to see the gap. Take a standard 1.8 × 1.8 m panel, painted on both faces, two coats:

1. Area per face: 1.8 × 1.8 = 3.24 m²; both faces = 6.48 m².
2. Two coats: 6.48 × 2 = 12.96 m² of coverage work.
3. Rough-sawn timber at a typical 7 m²/L: 12.96 ÷ 7 = 1.85 L per panel — call it 1.9 L, or 2.0 L with wastage.
4. Smooth planed timber at a typical 9 m²/L: 12.96 ÷ 9 = 1.44 L per panel — call it 1.5 L, or 1.6 L with wastage.

Scale that to a ten-panel run and the difference is real: roughly 20 litres for rough-sawn boards against 16 litres for planed panels. A fence paint coverage calculator that asks for the timber finish is doing exactly this division for you. Two practical notes: new pressure-treated timber often repels early coats until it has weathered for a few weeks, and sheds with back-boards, posts and gravel boards add 10–15% on top of the panel total.

Brand coverage: Dulux and Valspar per litre

Dulux typically states around 13 m² per litre on smooth interior walls; Valspar commonly sits around 12 m² per litre. Treat both figures as typical manufacturer guidance for smooth, primed surfaces rather than guarantees — real-world coverage falls with texture, porosity and strong colour changes, which is why the 10% wastage buffer stays in the calculation.

Both brands print the same style of figure on the tin, and both carry the same fine print. How to read a coverage label properly:

• Find the rate and its conditions. Dulux coverage per litre is typically quoted around 13 m² and Valspar around 12 m² — per coat, on a smooth, primed surface, at normal application. The words doing the work are "typically" and "smooth": a textured or bare surface will not hit them.
• "Up to" means best case. Marketing ranges quote the top of the laboratory result. Plan on the bottom of the range for rough surfaces and the middle for smooth ones.
• Opacity beats thinning. Better-pigmented paint reaches a uniform colour in two normal coats. Thinning premium paint to stretch it lowers the film weight and usually costs you a third coat — a false economy.

The gap between the brands is smaller than most people expect. Across our 38.6 m² example room, two coats at Dulux's typical 13 m²/L works out at 77.2 ÷ 13 = 5.94 L; at Valspar's typical 12 m²/L it is 6.43 L — about half a litre apart, less than the wastage margin. That is also why searches like "paint coverage calculator Dulux" or "Valspar paint coverage calculator" surface brand tools preloaded with these same rates: useful for their specific product ranges, still assuming smooth primed walls, and still needing your 10%.

Full worked example: a 4 × 5 m room

A 4 × 5 m room with 2.4 m ceilings, one 2 × 1.4 m window and one 0.9 × 2 m door presents 38.6 m² of wall per coat. At 12 m² per litre for two coats plus 10% wastage, the requirement is 6.43 × 1.1 ≈ 7.1 litres — so buy 7.5 litres.

Here is every step with the real arithmetic, no rounding shortcuts:

1. Perimeter. 2 × (4 + 5) = 18 m.
2. Gross wall area. 18 × 2.4 = 43.2 m².
3. Window. 2 × 1.4 = 2.8 m².
4. Door. 0.9 × 2 = 1.8 m².
5. Net wall area. 43.2 − 2.8 − 1.8 = 38.6 m².
6. Two coats. 38.6 × 2 = 77.2 m².
7. Paint at 12 m²/L. 77.2 ÷ 12 = 6.43 L.
8. Wastage. 6.43 × 1.1 = 7.08 ≈ 7.1 L.
9. Buy. 7.5 L — one 5 L tin plus one 2.5 L tin, with the remainder kept for future touch-ups.

The same room's ceiling (4 × 5 = 20 m²) in two coats at 12 m²/L needs 20 × 2 ÷ 12 = 3.33 L, and 3.33 × 1.1 ≈ 3.7 L — a 5 L ceiling tin covers it. Repainting a dark wall white? Assume three coats, not two: 38.6 × 3 ÷ 12 = 9.65 L, and with wastage roughly 10.6 L — effectively a second full tin. That is how quickly a colour change rewrites the shopping list.

When to use a paint coverage calculator

Use a paint coverage calculator whenever a job mixes surfaces, has several openings, or involves a strong colour change that forces extra coats — hand arithmetic multiplies small errors into empty tins. The free Toolfyra paint coverage calculator applies the formula above to walls, floors, fences and masonry in one pass and converts litres to gallons.

It earns its keep in four situations: mixed surfaces in one job (walls plus woodwork plus ceiling), more than two openings, a colour change that adds a coat, or a metric–imperial switch mid-project. Our paint coverage calculator runs the formula across all four surface types, adds the wastage margin automatically and rounds up to real tin sizes.

If you are still deciding between paint and wallpaper, run the numbers first — then preview both finishes on a photo of your own room with the wallpaper room preview tool before spending anything. For everything else in the same spirit, the home & decor tools hub and more free calculators keep the whole project in the browser — no signup, no uploads.