Paint Coverage Calculator

Calculate exactly how many litres of paint you need for any room or surface. Enter room dimensions and number of coats — includes doors, windows, and wastage allowance.

A paint coverage calculator estimates how many litres of paint you need to cover a surface area, based on the coverage rate of the paint (in m² per litre), the number of coats, and any wastage or surface porosity allowance. Getting paint quantities right avoids the cost of buying too much or the inconvenience of running out mid-job. Coverage rates vary significantly between paint types — from 6–8 m²/litre for thick masonry paint to 12–16 m²/litre for thin emulsion on smooth plasterboard. Tile & Flooring Calculator and Concrete Volume Calculator provide related area and materials calculation tools.

Surface preparation and texture have a major impact on actual coverage. Bare plaster, masonry, and rough wood are highly porous and absorb significantly more paint than previously painted surfaces — typically requiring a mist coat (heavily diluted first coat) before the full coverage rate applies. Always check the specific coverage rate on the paint tin label rather than relying on generic estimates.

Measure the surface area to be painted in square metres (width × height for each wall or surface).
Check the coverage rate on your paint tin label — typically expressed as "X m² per litre" for one coat.
Enter the number of coats — most jobs require 2 coats for even coverage; bare surfaces may need 3.
Add a wastage allowance of 10–15% for brush strokes, overlaps, and spillage.
Litres needed = (Area ÷ Coverage rate) × Number of coats × (1 + Wastage %)
Round up to the nearest tin size — paint is typically sold in 1L, 2.5L, 5L, and 10L tins.

Paint coverage formula

Litres needed = (Surface area m²) ÷ (Coverage rate m²/L) × Coats × Wastage factor

Surface area (room) = (2 × (Length + Width) × Height) − Door and window areas

Wastage factor = 1 + (Wastage % ÷ 100) — typically 1.10 to 1.15 (10–15%)

Worked example: Room 4m × 3m, 2.4m ceiling height. Wall area = 2 × (4+3) × 2.4 = 33.6 m². Subtract 2 doors (1.8 m² each) and 1 window (1.2 m²): net area = 33.6 − 3.6 − 1.2 = 28.8 m². Paint coverage 12 m²/L, 2 coats, 10% wastage: 28.8 ÷ 12 × 2 × 1.10 = 5.28 litres → buy 2× 2.5L tins (5L) or 1× 5L tin.

Reading your paint coverage result

Coverage rates by paint type

Typical coverage rates per coat: Silk/matt emulsion (smooth wall) 12–16 m²/L; Silk/matt emulsion (new plaster) 6–10 m²/L after mist coat; Masonry paint 5–8 m²/L; Gloss/satinwood (wood trim) 10–14 m²/L; Primer/undercoat 10–12 m²/L; Floor paint 5–8 m²/L; Garage floor paint 4–6 m²/L. Always use the figure on your specific tin — premium paints with higher pigment loading may cover more efficiently than budget alternatives at the same stated rate.

Construction tips and best practices

New plaster must be sealed with a mist coat (10% water : 90% emulsion dilution) before applying full-strength paint — bare plaster absorbs paint like a sponge and the mist coat halves effective coverage on the first pass.
Dark colours going over light backgrounds typically need 3 coats rather than 2 — factor this in, especially for bold or deep colours.
Calculate ceiling and walls separately as they may use different paints at different coverage rates (ceiling paint vs. wall emulsion).
Don't forget door frames, window reveals, and skirting boards if painting with a different colour — calculate these as separate line items.
Leftover paint stores well in an airtight tin in a frost-free location for touch-up jobs — buying slightly more than needed is often worthwhile.

A typical 3-bedroom semi-detached house requires approximately 30–40 litres of paint for a full interior redecoration across all rooms.
The average UK household redecorates a room every 5–7 years — paint represents one of the most cost-effective home improvement investments.
Professional decorators typically achieve 10–15% better coverage than DIY due to technique — they use less paint while achieving more even coverage with proper rolling method.
1 litre of standard emulsion paint covers approximately 12 m² per coat on smooth plasterboard — roughly the equivalent of a 3m × 1m wall section.

Common mistakes to avoid

Forgetting to deduct door and window areas from wall surface area — a typical room has 4–8 m² of openings that don't need paint.
Using the coverage rate without adjusting for surface condition — bare plaster, rough masonry, or weathered exterior surfaces absorb 30–50% more paint than smooth painted surfaces.
Buying exact quantities without wastage allowance — running out mid-wall and needing an emergency trip to the shop risks a colour batch mismatch on large areas.
Not accounting for multiple coats — manufacturer coverage rates are always per coat, not total; 2 coats of 12 m²/L paint on 24 m² requires 4 litres, not 2.

Paint coverage rates are guidance figures provided by manufacturers and vary by surface preparation, application method (brush, roller, spray), environmental conditions, and applicator technique. For commercial or new-build specifications requiring certified coverage rates and material quantities, always use manufacturer technical data sheets. Certain paints contain volatile organic compounds (VOCs) regulated under environmental legislation in the UK and EU — choose low-VOC or zero-VOC products where required by specification or regulation. This calculator is for planning and estimation purposes only.

Frequently Asked Questions

How much paint do I need for a room?

Calculate the total wall area (perimeter × height), subtract doors and windows, then divide by the paint's coverage rate (typically 10–12 m² per litre). Multiply by number of coats.

How many square metres does 1 litre of paint cover?

Coverage varies by product and surface texture, but most standard emulsion paints cover 10–12 m² per litre per coat on a smooth wall. Textured or porous surfaces may reduce this to 6–8 m².

How many coats of paint do I need?

A strong colour change usually needs 2 coats. White or light colours over white may need only 1. Dark colours or new plaster often require a primer plus 2 topcoats.

Do I need to include the ceiling in my paint calculation?

Yes, if you're painting the ceiling a different colour. Many calculators treat walls and ceiling separately. Ceiling paint typically has lower sheen and slightly different coverage.

What size paint tin should I buy?

Common sizes are 1L, 2.5L, 5L, and 10L. It's often more economical to buy one large tin than multiple small ones. Leftover paint can be resealed for touch-ups.