Paint Calculator
Estimate how many litres of paint a room needs. Enter dimensions or wall area, the number of coats, and coverage, and it subtracts doors and windows for you.
🎨 What is a Paint Calculator?
A paint calculator works out how much paint you need to cover the walls of a room, so you buy the right amount without running short or wasting money on extra tins. It takes the area you want to paint, multiplies by the number of coats, and divides by the paint's coverage rate to give the volume in litres. The result is the single most useful number before starting any decorating project.
Estimating paint by eye almost always goes wrong. Buy too little and you have to stop mid-job and hope the next tin matches; buy too much and you are left with half-used cans cluttering the garage. A quick calculation based on the actual wall area, the number of coats, and the coverage printed on the tin removes the guesswork. It is just as handy for a single feature wall as for a whole house repaint.
A common misconception is that you can paint over any surface with one coat. In reality two coats are standard, and light colours over dark, or paint on fresh plaster, often need three. Another mistake is forgetting to subtract doors and windows, which can add up to several square metres in a normal room. This calculator removes a typical door and window allowance automatically so your estimate reflects the area you will actually paint.
Enter your room dimensions, or the wall area directly, along with the number of doors and windows, the coats you plan to apply, and the coverage per litre. The calculator returns the paintable area, the total area across all coats, the exact litres required, and the whole number of litres to buy, with the full working shown.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — A Standard Bedroom
A 5 m by 4 m room with 2.5 m walls, 1 door and 2 windows, 2 coats
Example 2 — A Known Wall Area
40 m² of wall, 2 coats, coverage 10 m² per litre
Example 3 — A Large Living Room
A 6 m by 5 m room with 3 m walls, 2 doors and 3 windows, 2 coats
❓ Frequently Asked Questions
🔗 Related Calculators
How much paint do I need for a room?
Work out the wall area, multiply by the number of coats, and divide by the paint's coverage. For a 5 m by 4 m room with 2.5 m high walls, the wall area is about 45 m². After subtracting a door and two windows you get roughly 40 m², so two coats at 10 m² per litre need about 8 litres, meaning you should buy 9 litres.
How do you calculate wall area for painting?
Add the length of all walls and multiply by the height. For a rectangular room this is 2 × (length + width) × height. A 5 m by 4 m room with 2.5 m walls gives 2 × 9 × 2.5 = 45 m². Then subtract the area of doors and windows, which this calculator does using typical sizes of 1.8 m² per door and 1.5 m² per window.
How much does one litre of paint cover?
One litre of standard emulsion covers about 10 to 12 square metres per coat on a smooth, sealed surface. Rough, porous, or bare surfaces absorb more and reduce coverage, sometimes to 6 to 8 m² per litre. Check the tin, as coverage varies by brand and finish, and enter the correct figure for the most accurate estimate.
How many coats of paint do I need?
Two coats is standard for a durable, even finish. You may need three when painting a light colour over a darker one, covering fresh plaster, or using a thin or strongly pigmented paint. A single coat is usually only enough for a minor refresh of the same colour. This calculator lets you set the number of coats.
Should I subtract doors and windows?
Yes, for a more accurate estimate. Doors and windows are not painted with wall paint, so their area should be removed from the total. This calculator subtracts a typical 1.8 m² for each door and 1.5 m² for each window. If your openings are unusually large or small, adjust the counts or use the wall area mode with your own figure.
How much paint for a 12x12 room?
A 12 by 12 foot room is about 3.7 m by 3.7 m. With 2.4 m high walls the wall area is roughly 35 m². After subtracting a door and a window you get about 32 m², so two coats at 10 m² per litre need around 6.5 litres, meaning you should buy 7 litres. Enter your exact dimensions for a precise figure.
Does the calculator include the ceiling?
No, this calculator estimates wall paint only. Ceilings are usually painted with a separate ceiling paint. To include a ceiling, calculate its area as length times width and add it to your wall area using the wall area mode, or run a second calculation for the ceiling on its own.
Why should I buy more paint than the exact amount?
Buying a little extra covers touch-ups, spills, and areas that need a heavier coat, and ensures leftover paint matches the original batch. Because paint is sold in whole tins, this calculator rounds the litres up to the next whole litre so you always have enough to finish the job.
How do I convert square feet to square metres for paint?
Divide square feet by 10.764 to get square metres. So 350 square feet is about 32.5 m². Paint coverage is often quoted as around 350 square feet per gallon, which is close to 10 m² per litre. This calculator works in metres and litres, so convert your figures first if your measurements are imperial.
Does surface type affect how much paint I need?
Yes. Smooth, previously painted walls give the best coverage. Textured, porous, or bare surfaces such as new plaster, bare wood, and fresh drywall absorb more paint and cut coverage significantly. For these, lower the coverage figure you enter, or apply a primer or sealer coat first to reduce the amount of topcoat needed.