How Much Paint Do I Need? A Room-by-Room UK Guide
Direct Answer: In the UK, standard interior emulsion covers approximately 10 to 12 square metres (m²) per litre per coat. To calculate what you need, multiply your room perimeter by ceiling height, subtract doors (1.7 m²) and windows (1.5 m²), multiply by two coats, and add 10% for roller waste.
Few DIY dilemmas are as frustrating as running out of paint midway through a second coat on a Sunday afternoon—except, perhaps, overestimating your needs and being left with £80 worth of custom-tinted emulsion gathering dust in the garden shed. Estimating paint quantities accurately is essential for budgeting decorating projects, ensuring consistent colour batches, and preventing needless product waste.
While paint tins display manufacturer coverage estimates, real-world paint consumption depends on multiple variables: the porosity of your walls, whether the plaster is fresh or previously painted, the nap length of your roller, and whether you are making a dramatic colour change from dark to light.
This guide provides a dependable step-by-step formula for calculating paint requirements, breaks down standard coverage rates for leading UK brands like Dulux and Crown, provides a room-by-room reference matrix with exact tin recommendations, and explains how to handle challenging surfaces like fresh plaster.
What Is the Standard Paint Coverage per Litre in the UK?
Paint coverage in the UK is measured in square metres per litre (m²/L) per coat. For the vast majority of standard interior wall and ceiling emulsions, leading paint manufacturers quote an optimal spread rate of 12 m² to 14 m² per litre under laboratory conditions.
In real-world domestic decorating, however, roller absorption, wall texture, and application thickness reduce practical coverage. Professional decorators typically plan for 10 m² to 12 m² per litre per coat on previously painted, smooth surfaces.
Matt vs Silk and Satin Emulsion Spread Rates
- Matt Emulsion (10 – 12 m²/L): Flat finish that disguises minor wall bumps and surface imperfections; slightly thicker and more absorbent.
- Silk & Soft Sheen Emulsion (12 – 14 m²/L): Reflective sheen, durable, and easily washable; spreads smoothly across even surfaces.
- Eggshell & Satinwood (12 – 14 m²/L): Specially formulated for interior skirting boards, timber architraves, and doors.
- Exterior Masonry Paint (6 – 8 m²/L): Formulated for exterior brick and render; lower coverage due to rough textures.
Fresh Plaster and Porous Surfaces (The Mist Coat Rule)
Never apply standard, unthinned emulsion directly to bare, newly skimmed plaster. Fresh plaster is highly porous and will suck the moisture out of wet emulsion before the paint polymers bond, causing peeling later. Always apply a mist coat—diluting contract matt emulsion with 20% to 30% clean tap water. The coverage of a mist coat is approximately 6 m² to 8 m² per litre.
How to Calculate Wall Area and Paint Quantities (Step-by-Step)
Step 1: Measure Perimeter and Ceiling Height
Measure the length of all four walls in metres and add them together to get the perimeter. Multiply by ceiling height to obtain the gross wall area:
Gross Wall Area (m²) = Perimeter (m) × Height (m)
Step 2: Subtract Doors and Windows
Deduct surface areas taken up by openings:
- Standard single door: Deduct 1.7 m².
- Standard window: Deduct 1.5 m².
- Large patio or bay window: Deduct 3.0 to 3.5 m².
Step 3: Multiply by Number of Coats and Factor 10% Waste
Multiply net area by 2 (for two coats), multiply by 1.10 (10% roller/tray wastage), and divide by 12 m²/L to determine total litres.
Room-by-Room Paint Requirement Guide (Worked Examples)
| Room Type | Room Dimensions | Perimeter & Ceiling | Openings Deductions | Net Wall Area | Litres for 2 Coats | Recommended Tin Purchase |
|---|---|---|---|---|---|---|
| Small Bedroom / Box Room | 3.0m × 3.0m | 12.0m perim × 2.4m ht | 1 door, 1 window (3.2 m²) | 25.6 m² | 4.7 Litres | 1 × 5L tin |
| Medium Master Bedroom | 4.0m × 4.0m | 16.0m perim × 2.4m ht | 1 door, 1 window, 1 en-suite door (4.9 m²) | 33.5 m² | 6.1 Litres | 1 × 5L tin + 1 × 2.5L tin |
| Large Living / Dining Room | 5.0m × 6.0m | 22.0m perim × 2.5m ht | 2 doors, 1 bay window (6.5 m²) | 48.5 m² | 8.9 Litres | 2 × 5L tins (or 1 × 10L tub) |
| Standard Ceiling (Master Bed) | 4.0m × 4.0m | 16.0 m² ceiling area | No deductions | 16.0 m² | 2.9 Litres | 1 × 2.5L tin + 1 × 1L tin |
| Downstairs Cloakroom / WC | 1.5m × 2.0m | 7.0m perim × 2.4m ht | 1 door, 1 small window (2.5 m²) | 14.3 m² | 2.6 Litres | 1 × 2.5L tin + 1 × 1L tin |
UK Paint Tin Sizes: How to Buy Without Waste
In the UK, emulsion is sold in 1L, 2.5L, 5L, and 10L containers. A 5-litre tin typically costs only 25% to 35% more than a single 2.5-litre tin, making one 5L tin far better value than two 2.5L tins.
Frequently Asked Questions About Paint Quantities in the UK
How much wall area does 1 litre of paint cover in the UK?
One litre of standard UK interior emulsion paint covers approximately 10 to 12 square metres (m²) per coat on previously painted smooth surfaces. Unpainted fresh plaster or textured walls absorb more paint, reducing coverage to 6 to 8 m² per litre.
How many coats of paint are needed for a room?
Two coats of paint are standard for almost all interior domestic walls to ensure uniform colour depth and durability. If you are painting over a dark color with a light shade or painting fresh plaster, three coats (or a primer plus two coats) are usually required.
How do you calculate the paint needed for a ceiling?
To calculate ceiling paint, multiply the room's length by its width in metres to get the floor/ceiling area. Multiply by 2 for two coats, add 10% for roller spatter, and divide by 12 m² per litre. A 4m × 4m room ceiling requires approximately 2.9 litres of paint.
How much paint do I need for a 3m by 3m bedroom?
A 3m × 3m bedroom with standard 2.4m ceilings has a net wall area of approximately 25.6 m² after deducting one door and one window. For two coats, you need approximately 4.3 litres of emulsion, meaning one 5-litre tin is ideal.
What is a mist coat and how much paint does it use?
A mist coat is a primer layer applied to newly plastered walls, made by diluting standard matt emulsion with 20% to 30% clean water. Because fresh plaster is extremely porous, a mist coat covers around 6 to 8 m² per litre.
How much surface area do doors and windows take up?
A standard UK single interior door (1.98m × 0.76m plus architrave) accounts for approximately 1.7 m² of wall area. A standard domestic window accounts for around 1.5 m², while large bay windows or patio doors deduct 3.0 to 3.5 m².
Is it cheaper to buy one 5-litre tin or two 2.5-litre tins?
It is almost always significantly cheaper to buy one 5-litre tin. In UK hardware stores, a 5-litre tin of emulsion generally costs 25% to 35% less than buying two separate 2.5-litre tins of the exact same paint.
How much paint do I need for interior doors and skirting boards?
Woodwork gloss or satinwood typically covers around 12 to 14 m² per litre. One 750ml or 1-litre tin is usually sufficient to apply two coats to all skirting boards and door frames in an average-sized bedroom.
How much extra paint should I buy for wastage and touch-ups?
You should add a 10% allowance to your calculated paint volume. This covers paint absorbed by rollers and trays, minor wall surface irregularities, and provides a small leftover quantity for future scuff touch-ups.
How long does an opened tin of paint last?
Properly sealed water-based emulsion paint can last between 2 and 5 years if stored in a cool, dry place away from frost. Ensure the rim is thoroughly wiped clean and the lid is hammered down securely to create an airtight seal.