Free Online Calculators
Wall paint in litres: room size, windows, doors & coats
This calculator works out exactly how many litres of wall paint you need based on your room dimensions, windows, doors, and number of coats. It uses the standard coverage rate of roughly 10–12 m² per litre, adjusted for the areas you won't be painting. No more guessing at the DIY store.
Measure the width and height of each wall, multiply them for the area, add the walls together and subtract the openings such as doors and windows. Then divide that net area by the coverage stated on the paint tin and multiply by the number of coats.
Divide the coverage figure printed on the tin by the tin volume to get the paint needed per square foot for one coat. Smooth, sealed surfaces need less, while porous plaster, render or textured walls soak up noticeably more.
Coverage per gallon is stated by the manufacturer on the tin and varies with the product, the surface texture and the film thickness applied. Use that figure rather than a rule of thumb, and expect less coverage on bare, porous or heavily textured surfaces.
Paint quantity = (wall area − openings) × number of coats ÷ coverage per litre or gallon. Wall area is the perimeter of the room multiplied by the ceiling height; add the ceiling separately if you are painting it.
Enter the room dimensions, subtract doors and windows, choose the number of coats and the coverage rate of the product to get the volume of paint required. For a job estimate, add labour hours per square foot plus primer, filler, tape and covering materials.
A quart covers a quarter of the area given for a gallon of the same product, so check the coverage rate on the tin and divide by four. It suits accent walls, doors, trim and touch-ups rather than whole rooms.
For one coat on the walls of a small room like that, a gallon is usually enough once doors and windows are deducted. For two coats, or over a dark or unprimed surface, plan on more than one gallon.
A quart is generally not enough for all four walls of a room, even a small one. It is better suited to a single feature wall, a door, skirting boards or window frames.
Whether you're refreshing a single bedroom or renovating an entire house, knowing exactly how much paint to buy is one of the most important steps in any painting project. Buy too little and you risk running out mid-wall or facing colour mismatches between batches. Buy too much and you're wasting money on product you'll struggle to dispose of. Our free paint calculator takes the guesswork out of the equation entirely.
Our tool is designed to give you a precise estimate of the litres of paint needed for any room. It accounts for all the key variables that affect real-world paint consumption, delivering a reliable result in just a few seconds.
Once you enter these values, the calculator instantly displays the total litres of paint required, so you can walk into the hardware store knowing exactly what to buy.
Many homeowners underestimate the impact of small calculation errors. Consider a room that is 5 m × 4 m with a 2.5 m ceiling. The total wall area is 45 m². Subtract two standard windows (each 1.2 m²) and one door (1.8 m²) and you have roughly 40.6 m² to cover. With two coats at 10 m²/l coverage, you need approximately 8.1 litres. Rounding up to the nearest available tin size (for example, two 5-litre tins) ensures you have enough without massive overspend.
Leftover paint is classified as hazardous waste in many countries and cannot simply be thrown in the bin. Proper disposal often costs money. By calculating your needs accurately, you minimise waste and contribute to a more sustainable approach to home improvement. Our free paint calculator is your first step toward a smarter, greener renovation.
A child's room measuring 3.5 m × 3 m with a 2.4 m ceiling has roughly 31.2 m² of wall area. With one window and one door removed, the net area drops to about 27 m². Two coats at 10 m²/l means you need 5.4 litres — one standard 5-litre tin and a small top-up tin should cover it perfectly.
Larger open-plan spaces can feel daunting to estimate. A room that is 8 m × 5 m with a 2.7 m ceiling has a wall area of around 70.2 m². Even with several large windows and doors subtracted, you're likely looking at 55–60 m² of paintable surface — requiring 11–12 litres for two coats at standard coverage.
Older homes often feature ceiling heights of 3 m or more. This dramatically increases wall surface area compared to modern properties. A room that appears modest in floor area can require significantly more paint than expected. The calculator handles non-standard ceiling heights effortlessly.
Add up the perimeter of the room (all four wall lengths combined) and multiply by the ceiling height. Then subtract the areas of windows and doors. Our paint calculator does all of this automatically when you enter your room dimensions.
At a standard coverage of 10 m²/l, you'd need 3 litres for one coat or 6 litres for two coats. Always check the specific coverage rate printed on your chosen paint tin, as this can vary between products.
Our calculator focuses on wall surfaces. To calculate ceiling paint separately, enter the room's floor area (length × width) as an additional surface, or use the calculator a second time with those dimensions.
Coverage rate (or spreading rate) tells you how many square metres one litre of paint will cover on a smooth, prepared surface. It is always printed on the tin. Higher-quality paints often have better coverage, meaning you use less product overall.
Yes — if you're applying a light colour over a similar existing shade on a well-prepared surface, one coat is often sufficient. However, for colour changes, especially from dark to light, or for bright feature wall colours, two coats are almost always needed for a consistent, professional result.