Enter your room and opening sizes to estimate colour paint and primer separately, then round each product up to tins you can buy.
For walls 2.4 m high, one 0.9 x 2 m door and two 1.2 x 1.2 m windows, the wall area is 43.20 - 1.80 - 2.88 = 38.52 m2. The ceiling is excluded.
Two colour coats at 11 m2/L need 7.00 L before allowance: buy 3 tins of 2.5 L. One primer coat at 10 m2/L needs 3.85 L: buy 2 tins of 2.5 L. These are separate products.
If you choose 10% extra, colour becomes 7.704 L, which rounds up to 4 tins. Rounding to whole tins can make a small allowance change the purchase quantity.
Use the m2 per litre per coat stated for the paint and surface you have chosen. Coverage depends on both the product and the surface. The starting values here are editable examples, not a product specification.
Opening area equals count x average width x average height. Enter measured sizes. If openings differ, choose averages whose width x height equals the mean opening area, or calculate sections separately. Reveal surfaces and trim are not included.
Follow the selected product instructions for your surface and colour change. The calculator lets you choose colour and primer coats separately. Some paints specify a one-coat system; there is no universal two-coat rule.
Primer has its own coverage, coat count and tin size. Enabling it applies those values to the same area as the colour paint. Estimate it separately if only part of the room needs primer.
It is an optional percentage added before each product is rounded up to whole tins. Leave it at zero for the geometric estimate. Choose any additional allowance based on your own project and product guidance.
Product guidance: Dulux coverage calculator notes and Dulux coat and quantity guidance. Use the current instructions for the product you buy.
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