How much paint do I need? Paint calculator

Paint calculator: room walls or measured area

How do you measure a room for paint?

For four rectangular walls of equal height, add the room's length and width, double that total and multiply by the wall height. This gives wall area, not floor area. A 4 m by 3 m room with 2.4 m walls has 33.6 m² of wall before deductions: 2 × (4 + 3) × 2.4.

Measure doors and windows by width × height and add those areas if you want to exclude them. Only deduct surfaces that will not receive this paint. Include painted reveals as separate measured surfaces where needed. If you leave openings undeducted, the estimate already includes some spare area; remember that before adding a large extra allowance.

For an L-shaped room, alcoves or walls of different heights, measure each actual wall face and add them. Use the calculator's measured-area option. For a triangular wall portion, its area is half its base × vertical height. Do not use the bounding rectangle for a complicated room and assume it represents the painted surfaces.

A feature wall needs only that wall's area. A flat ceiling is length × width; calculate it separately if it uses a different paint. Measure sloping ceilings along the surface itself. For inaccessible heights or stairwells, arrange safe measurement and access rather than overreaching to obtain a figure.

The paint quantity formula and a worked example

Litres before allowance = net area in m² × coats ÷ coverage in m² per litre. Then multiply by 1 + allowance ÷ 100 if you want extra paint. This follows the area, coats and product-coverage method explained by Dulux. The allowance is a separate planning choice.

Here is the example loaded by the calculator's example button. These are illustrative measurements, not a standard size or a promise that every bedroom takes this much paint.

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The ceiling in this room is another 12 m². At the same example coverage and two coats, it needs 2 litres before allowance, or 2.2 litres with 10% extra. If the ceiling uses a different product, that quantity cannot be taken from the wall-paint total. Woodwork and primer are separate too.

How much does 5 litres of paint cover?

At an example coverage of 12 m² per litre per coat, 5 litres covers 60 m² once, or 30 m² with two coats, before losses or any spare allowance. Use the actual rate printed on the product: 5 litres of one coating can cover a different area from 5 litres of another.

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These are arithmetic examples, not coverage claims for a named product. An 'up to' coverage figure depends on the substrate and application conditions. Check whether the figure is per coat and whether the surface needs its own primer. Do not spread paint too thinly simply to make the tin last.

The Dulux calculator likewise asks for the chosen product because coverage and recommended coat count vary. Our calculator leaves both editable, so you can use the instructions for the paint you actually intend to buy.

How many coats and how much extra paint?

Start with the coating manufacturer's instructions for the substrate and existing finish. Two coats is the calculator's example, not a rule for every paint. A change from a strong dark colour, repaired patches or an uneven base can affect the system required. Resolve preparation before treating more finish paint as the solution.

The optional allowance can cover a chosen margin for application losses, small measurement differences or future touch-ups. Ten per cent is only the starting example; it does not guarantee enough for a rough, porous or unusually shaped surface. If the product gives different coverage for that surface, use that figure rather than hiding the difference inside an arbitrary allowance.

New plaster may need a specified primer or mist-coat system. Calculate that separately using its own coverage and dilution instructions: adding water does not give you more finish paint at its undiluted coverage. See painting new plaster and preparing walls for paint.

If a wall already looks uneven, use the patchy-paint checks before ordering another tin. Coverage, sheen differences and surface defects are different problems. A litre estimate cannot diagnose them or determine the drying time between coats.

Which tin sizes should you buy?

The result rounds upward to the next 0.1 litre for planning. Choose available tins of the same product, colour and finish whose combined volume meets that amount. The tool does not round everyone up to a large tin because available sizes and prices vary.

For the 5.5-litre example, a 5-litre tin alone falls short of the selected allowance. If matching 1-litre and 5-litre tins are available, they total 6 litres. If the paint comes only in 2.5-litre and 5-litre sizes, 7.5 litres is another combination. Compare the actual options rather than assuming the largest tin is cheapest or necessary.

Check existing paint before subtracting it from your shopping list: it needs to be the correct product and finish, usable, and sufficient in quantity. Record the colour reference and product details for later touch-ups. Different ages or batches may still produce a visible difference, so discuss the finishing approach before painting adjoining areas from separate supplies.

For several rooms using the same paint, calculate each room and add the litre requirements before buying. Keep separate totals for feature colours, ceilings, trim and primers. The room-refresh planning article helps order repairs and coating stages.

How does paint quantity affect a decorating quote?

Litres estimate material quantity, not labour time. Preparation, protection, cutting in, access, repairs, coat count and return visits all affect the work. A small wall with damaged paint may take more preparation than a larger sound wall.

For a CHS painting and decorating quote, send the room dimensions, surfaces, condition, paint details and photos. The Wimbledon page covers planning a room refresh alongside fittings and furniture; the East Sheen page explains smaller wall and woodwork enquiries. A postcode identifies the visit location; the actual surfaces determine the paint requirement.

Labour rates and materials are separate. Use the pricing guide for the confirmed minimum, additional time and materials calculation. Agree who supplies paint before ordering, especially when several products or drying stages are involved.