Paint Calculator

Last updated: June 2026

Room type

Room length

Room width

Room height

Doors

doors

Windows

windows

Number of coats

Paint type

Area to paint

30.3 m²

Paint needed

5.51 litres

Buy

1 x 5L, 1 x 1L

Formula

Wall area = 2 x (length + width) x height. Deductions = doors x 1.8m² + windows x 1.5m². Litres = paintable area x coats / coverage.

Typical UK paint coverage

Paint type	Coverage
Emulsion	10-12 m² per litre
Gloss	8-10 m² per litre
Masonry paint	Around 5 m² per litre
Undercoat	Around 8 m² per litre

About this calculator

Estimate how many litres of paint to buy for a single wall, a whole room, a ceiling, or a room plus ceiling. The calculator is useful before visiting a DIY store because it turns wall dimensions, doors, windows, coats, and paint coverage into a practical tin recommendation.

Paint quantity method

The calculator uses metric dimensions and practical UK planning assumptions. Results are estimates, so check product labels, site conditions, and supplier guidance before ordering materials.

wall area = 2 x (room length + room width) x room height
deductions = doors x 1.8m² + windows x 1.5m²
litres needed = paintable area x coats / coverage rate

How to use the paint calculator

Choose the project type or measurement mode where the calculator offers one.
Enter all dimensions in metric units.
Add allowances such as coats, waste, pattern repeat, roll width, or bag size where relevant.
Review the main highlighted result first.
Check secondary results such as packs, bags, rolls, posts, or tin combinations.
Round up to supplier pack sizes and confirm the label coverage before buying.

Worked examples

Medium bedroom walls

Input: 4m x 3m room, 2.4m high, 1 door, 1 window, 2 coats, matt emulsion at 11m²/L

Calculation: Wall area 33.6m² - 3.3m² deductions = 30.3m². Two coats = 60.6m².

Result: About 5.51 litres, so a 5L tin plus a small top-up or a larger tin is sensible.

Single feature wall

Input: 4m wide by 2.4m high, 2 coats, emulsion at 10m²/L

Calculation: Area 9.6m² x 2 coats = 19.2m². 19.2 / 10 = 1.92L.

Result: A 2.5L tin usually covers the wall with a small margin.

Paint coverage rates explained

Coverage varies by paint type, brand, surface condition, colour change, roller, and how heavily the paint is applied. UK wall emulsion commonly covers around 10-12m² per litre, while gloss, undercoat, and masonry paint often cover less.

Fresh plaster, porous masonry, textured walls, and dark-to-light colour changes may need more paint than a simple calculator estimate. Always check the tin label before buying.

How many coats do I need?

Two coats is the normal planning assumption for interior walls. One coat may work for a refresh in a similar colour, while three coats may be needed for dramatic colour changes, patchy walls, or lower-opacity paint.

Emulsion vs silk vs matt

Matt emulsion gives a flatter finish and can hide imperfections. Silk emulsion is shinier and more wipeable. Gloss and satinwood are usually used for woodwork rather than broad wall areas, so their coverage rates and project use are different.

Common mistakes

Mixing centimetres, millimetres, and metres without converting first.
Ordering exact quantities with no allowance for cuts, waste, damage, or uneven surfaces.
Forgetting that products are sold in tins, packs, bags, rolls, or boards rather than exact calculated quantities.
Using average deductions or coverage rates when the project has unusual shapes, textures, slopes, or access limits.
Not checking manufacturer instructions before final ordering.

Home improvement estimate disclaimer

This calculator is for general DIY planning only. It is not a substitute for a professional survey, structural design, building control advice, manufacturer instructions, or installer measurement.

Actual product coverage and pack sizes vary by supplier.
Site conditions can change material quantities.
Structural, roofing, electrical, gas, and regulated building work may need qualified advice.

Frequently asked questions

Should I subtract doors and windows?

Yes for whole-room wall estimates. The calculator uses 1.8m² per door and 1.5m² per window as practical defaults.

Should I buy exactly the calculated litres?

Usually no. Paint is sold in tin sizes, and a little spare helps with cutting in, touch-ups, roller loading, and uneven surfaces.

Does ceiling paint use the same coverage?

Often it is similar to matt emulsion, but check the product label. Textured or previously unpainted ceilings can need more paint.

Why does masonry paint need more litres?

Exterior masonry is usually more porous and textured than interior plaster, so coverage per litre is lower.

Can this replace the paint brand calculator?

Use this for planning. For final buying, compare it with the coverage printed on the exact tin you plan to buy.

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What does this mean?

This calculator is designed to help you understand the likely number before you make a decision or start an application.

Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.

Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.