Paint Calculator

Free Paint Calculator – Estimate How Much Paint You Need for Any Room or Wall

One of the most common mistakes people make when starting a painting project is buying the wrong amount of paint. Buy too little and you are running back to the store mid-job, hoping the next batch is an exact color match. Buy too much and you end up with half-used tins collecting dust for years. This free online paint calculator takes the guesswork out completely. Enter your room dimensions and the coverage rate of the paint you are using, and get an accurate estimate of exactly how many litres you need to buy.

Why Getting the Paint Quantity Right Matters

Paint is sold in fixed tin sizes — typically 1L, 2.5L, 5L, and 10L — so even being slightly off in your estimate can mean buying an extra full tin. On premium paint that can mean spending an extra £20–30 unnecessarily. Getting as close as possible to the right amount saves money, reduces waste, and avoids the frustration of a mid-job color mismatch if a new batch is from a different production run.

The amount of paint needed depends on several factors: the total surface area, the number of coats you are applying, the spread rate of your specific paint, and the porosity of the surface. This calculator lets you account for all of those variables.

How the Paint Calculator Works

The calculation is straightforward. The tool multiplies your wall width by height to get the area, subtracts any allowance for doors and windows, and then divides the total paintable area by the spread rate of your paint (measured in square metres per litre). Multiply by the number of coats and you get the total paint volume required.

1. Enter the width and height of each wall or surface you plan to paint.
2. Subtract area for doors and windows where relevant.
3. Specify the number of coats — most interior walls need two for full, even coverage.
4. Enter the coverage rate from your paint tin (usually shown as m² per litre on the label).
5. Get an instant estimate in litres, plus guidance on the most economical tin size to buy.

Factors That Affect How Much Paint You Need

• Surface texture — Rough or textured surfaces absorb significantly more paint than smooth plastered walls. Always add extra for textured finishes.
• Paint type and finish — Matt emulsions typically cover 10–12 m² per litre. Silk and satin finishes cover 11–13 m² per litre. Gloss covers more but goes on thinner. Masonry paint varies considerably by surface porosity.
• Color change — Going from a dark color to a much lighter one (or vice versa) may require an extra coat, especially with lighter pastel shades that have lower pigment density.
• New plaster — Freshly plastered walls are highly absorbent. They need a diluted mist coat first (typically 10% water mixed in), which soaks in rather than sitting on top. Always account for this additional coat on new plaster.
• Age of existing paint — Old, chalky, or flaky surfaces absorb more than well-maintained painted walls.

Standard Paint Coverage Rates

Coverage varies by paint type. As a general guide for planning purposes:

• Matt emulsion: 10–12 m² per litre
• Silk or satin emulsion: 11–13 m² per litre
• Exterior masonry paint: 5–8 m² per litre (highly variable by surface)
• Satinwood or gloss: 12–15 m² per litre
• Undercoat or primer: 8–10 m² per litre

Always use the coverage figure printed on your specific tin for the most accurate result. Premium paints often offer better coverage than budget options, so the brand matters.

Common Painting Projects This Calculator Helps With

• Bedroom, living room, or kitchen repaint
• Full house interior before moving in or letting
• Feature accent walls
• Exterior rendering and masonry
• Estimating materials for a contractor quote
• Garage, shed, or outbuilding painting

Whether you are a homeowner tackling a weekend DIY project or a decorator planning multiple rooms for a client, this paint calculator gives you the right number before you head to the store. Run the estimate first, buy the right amount, and start painting with confidence.