Paint Calculator
Calculate how much paint you need for any room. Enter dimensions, deduct doors and windows, choose paint type and number of coats. Get tin sizes and cost estimates.
Room Dimensions
Openings & Coverage
~1.9 m² each
~1.5 m² each
Paint Price
Tin Sizes
Results
Total Wall Area
33.60 m²
Paintable Area
30.20 m²
Litres Needed
6L
Estimated Cost
£48.00
Recommended Tins
Litres, Coats and Coverage You Can Trust
Most emulsion paints cover about 12 m² per litre on a smooth, previously painted wall. Two coats is the realistic standard; one coat almost never delivers the colour shown on the tin. The default room here, 4m by 3m by 2.4m high with one door and one window, has a paintable area of around 30.2 m². At 12 m² per litre and two coats, you need 6 litres - so one 5L tin and one 2.5L tin, totalling £60 at £8 per litre.
Coverage drops sharply on porous or dark surfaces. Fresh plaster soaks the first mist coat at roughly 6 to 8 m² per litre. Going from a deep teal to brilliant white might genuinely need three coats. Textured walls eat 20 percent more paint than the tin promises. The calculator lets you adjust coverage downward when reality bites; do not trust the default of 12 m² per litre on a chalky old wall that has not seen paint in fifteen years.
Tin Sizes and What to Buy
Trade tins come in 2.5L and 5L mostly; specialist or designer brands sometimes only offer 2.5L. Always round up to whole tins. A 6-litre requirement means buying 7.5L (one 5L plus one 2.5L), not opening two 5L tins and trying to store a half-used pot for two years. Once a paint tin is opened, it skins over within months even with a good seal, and most decorators write off any remainder beyond six months.
Keep one labelled jam jar of each colour in the cupboard for touch-ups: a tablespoon decanted at the end of the job covers chips, scuffs and small marks for years. Doors typically need 0.5L for two coats. Skirting boards and architrave for a standard room run around 1L. The calculator focuses on walls, but factor those extras in when you order, especially for a full room repaint.
Frequently Asked Questions
How many coats of paint do I need?
Two coats is standard for emulsion over a previously painted wall in a similar shade. Fresh plaster needs a thinned mist coat first, then two full coats - so three coats total. Going from very dark to very light or vice versa often needs three full coats unless you use a tinted primer first.
How much paint do I need for one wall?
Multiply the wall height by width to get area in m². Divide by 12 (typical coverage per litre) and multiply by the number of coats. A 4m x 2.4m wall is 9.6 m². Two coats at 12 m² per litre is 1.6 litres - round up to a 2.5L tin.
Can I store leftover paint?
Sealed properly and stored above freezing, opened tins keep usable for six to twelve months. Decant a small jam jar's worth for future touch-ups; the smaller air gap dramatically extends life. Frozen paint is ruined; never store paint in an unheated garage or shed over winter.
What is a mist coat?
A mist coat is the first layer over fresh plaster, using emulsion thinned roughly 70 percent paint to 30 percent water. Plaster is highly absorbent; the mist coat soaks in and seals the surface, so the next two full coats lay down evenly without patchiness. Skip it and the topcoat will dry inconsistently.
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