Calculate your paint
How to calculate paint for a room
Start by measuring the room length, width and wall height. This calculator assumes four straight walls forming a rectangular room. If your room has an unusual shape, calculate separate sections and add their paint quantities.
Step 1: Calculate the wall area
Wall area = 2 × (length + width) × height. Subtract the total surface area of doors and windows you will not paint. If you are painting the ceiling with the same product, add length × width.
Step 2: Allow for coats and coverage
Multiply the net paintable area by the number of coats. Divide by the paint's stated coverage per litre or per US gallon. Coverage depends on the paint, surface texture, porosity and application method. Use the number printed on your chosen paint product.
Step 3: Add waste and round up to full tins
Add your chosen extra percentage, then divide the paint volume by the size of one tin or can. Round up to the next whole container. Multiply that count by the price per container to estimate paint purchase cost.
Worked example: UK room
A 4 m × 3 m room with 2.4 m walls has 33.6 m² of wall surface. Subtract 4 m² for openings to get 29.6 m². For two coats at 10 m² per litre, you need 5.92 L before waste. With 10% extra, the estimate is 6.512 L. Buying 2.5 L tins means three tins, or 7.5 L purchased. At £25 per tin, the estimated paint cost is £75.
What the estimate includes and excludes
The result covers paint for the selected wall area and optional ceiling, using one coverage rate and container size. It does not include primer, separate trim paint, brushes, rollers, labour, delivery or tax. Different products for ceilings and walls should be estimated separately. Rough plaster, deep colours and fresh surfaces sometimes need extra coats or primer. Always check the manufacturer's instructions.
Frequently asked questions
How many coats should I enter? Two coats is a common planning example, but follow your paint manufacturer's guidance and check whether a primer is needed.
Does this calculate US or imperial gallons? US mode uses US liquid gallons. One US gallon is approximately 3.785 litres. UK mode uses litres.
What if I have several rooms? Calculate each room separately, then combine the required paint volumes if using the same paint. Round container purchases after combining volumes to avoid unnecessary tins.
Will changing the currency convert my price? No. Enter the actual local price per container. The selector changes only the displayed currency symbol.
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