Paint Calculator — How Much Paint Do I Need?

How to Calculate Paint for a Room

Knowing exactly how much paint to buy is one of the simplest ways to save money on any decorating project. Whether you are refreshing a single room or repainting your entire house, our paint calculator uses real coverage data from UK manufacturers to give you an accurate estimate.

Understanding Paint Coverage Rates

Paint coverage — the area one litre will cover in a single coat — varies significantly between paint types, brands and surface conditions. The figures below represent typical coverage rates for UK paints applied to a smooth, sealed surface:

Do I Need Primer?

Primer is not always necessary, but there are several situations where it is essential for a professional finish:

• New plaster: Apply a mist coat first — a 50/50 mix of emulsion and water (or Dulux Trade Supermatt diluted 10-20%). This seals the plaster and provides a key for the topcoat. Never apply full-strength emulsion to new plaster as it will peel.
• Bare wood: Use a dedicated wood primer such as Zinsser BIN or Dulux Trade Quick Dry Wood Primer. This seals the grain, prevents tannin bleed and ensures even absorption.
• Covering dark colours: A grey-tinted primer (like Zinsser Cover Stain) under light paint saves you buying extra coats. Going from dark blue to white without primer could need 4-5 coats; with primer, you typically need just 2.
• Stained surfaces: Water stains, nicotine, felt-tip pen and other persistent stains require a shellac-based primer like Zinsser BIN before painting.
• Switching paint types: If going from oil-based to water-based paint, an adhesion primer is recommended to prevent peeling.

Paint Types Explained

Choosing the right type of paint for each surface is just as important as calculating the right quantity. Here is a quick guide to the main types available in UK DIY stores:

Matt emulsion is the most popular choice for walls and ceilings in the UK. It has a flat, non-reflective finish that hides minor imperfections in plaster and dries quickly. Modern matt emulsions from brands like Dulux, Crown and Leyland are wipeable, making them suitable for most rooms.

Silk emulsion has a subtle sheen that is easier to clean than matt. It is traditionally used in kitchens and bathrooms, though it does highlight surface imperfections more than matt. The slight shine makes rooms feel brighter.

Eggshell has a mid-sheen finish between matt and silk. It is increasingly popular for woodwork as a modern alternative to gloss, offering a sophisticated look with good durability. Little Greene and Farrow & Ball both produce excellent eggshell finishes.

Gloss provides a highly reflective, hard-wearing finish primarily used for woodwork — skirting boards, door frames and architraves. Water-based gloss (acrylic) has largely replaced oil-based in the UK market, offering lower VOC emissions and faster drying times, though some decorators still prefer oil-based for its superior levelling.

Wall Preparation for Best Results

Proper wall preparation is the single most important factor in achieving a professional paint finish. Even the most expensive paint will look poor on a badly prepared surface. Follow these steps:

1. Fill cracks and holes: Use a ready-mixed filler (such as Polyfilla) for small cracks and a two-part filler for larger holes. Sand smooth once dry.
2. Sand the surface: Lightly sand previously painted walls with 120-grit sandpaper to provide a key for the new paint. Use a sanding block for flat surfaces.
3. Clean the walls: Wash with sugar soap solution to remove grease, dust and grime. This is especially important in kitchens and bathrooms.
4. Mask off edges: Use good-quality masking tape (Frog Tape is the UK favourite) along skirting boards, window frames and ceilings for crisp lines.
5. Protect floors and furniture: Lay dust sheets — cotton dust sheets are reusable and more eco-friendly than plastic.

UK Paint Tin Sizes and Value

Paint in the UK is sold in standardised tin sizes. The cost per litre decreases significantly as the tin size increases, so buying larger tins is almost always better value:

For the best deals on paint in the UK, check B&Q, Wickes, Screwfix and Dulux Decorator Centres. Trade paint (such as Dulux Trade or Crown Trade) is also available to the public and often represents better value per litre with superior coverage and durability.

How Many Coats Do I Need?

The number of coats you need depends on several factors:

• Same colour or similar shade: 2 coats is standard for a refreshed, even finish
• Light over light: 2 coats usually suffices
• Light over dark: 2-3 coats, or use a primer first
• Dark over light: 2 coats is usually sufficient as dark paint has high opacity
• New plaster: Mist coat + 2 full coats = 3 coats total
• Woodwork (gloss/satin): Primer + undercoat + 2 topcoats for bare wood; 1-2 topcoats for previously painted wood

Frequently Asked Questions