How much paint should you allow for a room?

Area, number of coats and product coverage are enough to establish an initial consistent estimate.

Measure the usable area

For a rectangular room measuring 5 m by 4 m with 2.5 m-high walls, the perimeter is 18 m. The gross area of the four walls is therefore 18 × 2.5 = 45 m². If doors and windows account for 4 m², the area to paint becomes 41 m². Measure openings instead of using an arbitrary estimate. The ceiling is calculated separately: here it covers 20 m².

Read product coverage

Coverage indicates the area covered per litre, usually for one coat under stated conditions. If the tin says 10 m²/L and you plan two coats on 41 m², the calculation gives 41 × 2 ÷ 10 = 8.2 L. Use the coverage of your chosen product, because paints and substrates can lead to different consumption. The figure suggested by the tool is simply an example.

Separate theoretical quantity from the order

An order should account for available pack sizes, touch-ups and losses. A theoretical need for 8.2 L does not mean that pack size exists. Compare available combinations of tins and keep an allowance suited to the job. Do not add the same reserve twice: if your measurement already includes an allowance, note it clearly to avoid an excessive surplus.

Identify the estimate's limitations

A porous wall, a marked colour change or uneven application may increase the quantity needed. A primer may also be a separate item. The calculator estimates a quantity; it does not determine the appropriate paint system for the substrate. Consult the manufacturer's instructions for preparation, coats, application conditions and drying. For the budget, then add tools, protection and any labour costs.

Put it into practice

• Wall area
• Paint quantity
• Renovation budget

Educational text prepared with AI assistance. The examples use adjustable assumptions and are not personal advice.