100% free · Runs 100% in your browser · Instant calculation · No signup needed
How it works: wall area = 2 × (length + width) × height, minus 2 m² per door and 1.5 m² per window, then multiplied by the number of coats. Litres = paintable area ÷ coverage. Cans are rounded up — you cannot buy part of a can — and cost = litres × price per litre. Tip: buy about 10% extra for touch-ups and for porous or unprimed walls, which drink more paint than the label coverage suggests.
Try an example: 5 m × 4 m room, 2.7 m high, 2 coats
A paint calculator is a simple planning tool that answers one practical question before you visit the paint store: how much paint do you actually need? Instead of guessing, counting cans in the aisle, or buying extra paint just in case, you enter the size of your walls, subtract the parts you will not paint, and get an estimate of the litres required. The result helps you budget sensibly, avoid wasted paint, and make sure you do not run out halfway through the final wall. Whether you are repainting a single bedroom, refreshing a whole house, or pricing a job for a client, a quick calculation at the start saves money, time, and return trips to the store.
Painting projects are easy to underestimate. A room that looks small can still have a surprising amount of wall surface once you add up all four walls, and doors, windows, and built-in cupboards all change the total. A paint calculator removes the guesswork by turning measurements into a clear number you can act on.
The maths behind the tool is straightforward, and it follows the same steps a professional decorator would use when estimating a job. First, the paintable area of a single wall is its length multiplied by its height. A wall that is 5 metres long and 2.6 metres high has a paintable area of 13 square metres. The tool repeats that calculation for every wall you add and sums the results. Then it subtracts the area of doors and windows, because you will not be painting over those openings. Finally, it divides the remaining area by the coverage rate of the paint, which is the number of square metres one litre covers, to find the litres needed.
Using the tool takes only a few minutes. You will need a tape measure, the approximate size of any doors and windows in the room, and the coverage figure from your chosen paint.
Suppose you are painting a room with four walls. Two walls measure 4 metres by 2.5 metres, giving 10 square metres each, and two walls measure 3 metres by 2.5 metres, giving 7.5 square metres each. The total wall area is therefore 35 square metres. The room has one door of 2 square metres and one window of 1.5 square metres, so subtracting 3.5 square metres leaves a paintable area of 31.5 square metres. If your paint covers 10 square metres per litre, you need 3.15 litres, which rounds up to 4 litres. If the paint is sold in 5-litre cans, one can covers the job for a single coat. For two coats you would need 8 litres, so two 5-litre cans would do the job with a little left over for touch-ups.
Paint is sold in whole litres and whole cans, and you cannot buy a fraction of a can. Rounding up also leaves a small margin for touch-ups, spills, and the extra absorption of the first coat, which always soaks into the surface more than later coats. Running out mid-project is worse than having a little left over: a new can from a different batch can dry to a slightly different shade, leaving a visible patch on the wall. A small surplus is genuinely useful for future scuffs and marks, so rounding up is the practical choice, not just a mathematical one.
Coverage varies by product, surface, and the number of coats, so no calculator can promise an exact figure for every paint and every wall. The default coverage figure in this tool is an example only and must be editable, because your paint may cover more or less than the default suggests. Primer, dark colours, and rough surfaces all need more paint: bare plaster drinks in the first coat, deep colours often need an extra coat for even coverage, and textured or rough surfaces hold more paint than smooth ones. Always check the coverage stated on your chosen product and adjust the figure in the tool to match it. If you are painting over a very dark colour with a light one, or working on unprimed plaster, budget for an extra coat before you buy.
Planning a project like this is easier when your everyday tools are sorted too. If you are building a website for your painting business, portfolio, or side project, FistHost shared hosting starts at just $0.99/month, and every annual plan includes a free domain, so you can get your business online without a big upfront cost.
It depends on the product. Most interior paints cover around 8 to 12 square metres per litre per coat, but you should always use the figure printed on your tin. Enter that figure into the calculator rather than relying on the default, especially for primer or specialist finishes.
Yes, for an accurate estimate. Doors and windows are not painted with wall paint, so their area should come off the total. In a room with several large windows, skipping this step can overstate the paint needed by a full can or more.
The result depends on the number of coats you enter. Two coats roughly double the paint needed, and dark colours or bare surfaces may need a third coat. Always plan your coats before buying, and remember that primer counts as its own coat on new surfaces.
Paint is sold in whole cans, and rounding up leaves a margin for touch-ups and absorption. A small surplus is far more useful than running out halfway through the last wall and risking a shade difference from a new batch.
Once your painting project is done, put the result to work online. With FistHost shared hosting at $0.99/month and a free domain with an annual plan, you can publish photos of your work, take enquiries, and grow a small business website without technical hassle.
A paint calculator turns a tape measure and a few numbers into a confident shopping list. Measure your walls, subtract the openings, match the coverage rate to your chosen paint, and round up. With that simple routine, you will buy the right amount, waste less, and finish the job without an emergency trip to the store. For quick conversions between metres, feet, and litres while you measure, try the Unit Converter, check your room maths with the Scientific Calculator, and work out discounts on paint with the Percentage Calculator.
No reviews yet. Be the first to review this tool!
Reviews are protected by captcha and moderated before they appear.