How the Paint Coverage Calculator Works
The calculator works out the paintable wall or ceiling area from your measurements, subtracts doors and windows, then allows for the number of coats required. It uses the typical coverage rate for your selected paint type to estimate how many litres of paint you’ll need.
How to Use the Paint Coverage Calculator
Using the calculator only takes a few steps:
- Choose what you’re painting — a single wall, all walls, or the walls and ceiling.
- Enter your measurements — add the room length, width and height in metres.
- Add doors and windows — these are deducted from the paintable area automatically.
- Choose your paint type — select the option that best matches the paint you plan to use.
- Select the number of coats — two coats are typical for most decorating projects.
- Calculate your paint — the tool will estimate how many litres you need and suggest a practical tin size.
For the most accurate result, use your actual room measurements and check the coverage stated on your chosen paint, as this can vary between products.
Typical Paint Coverage Rates (UK)
Paint coverage can vary between brands, finishes and surface types, so these typical UK figures provide a useful baseline when estimating how much paint you’ll need.
Average Coverage per Litre
| Paint Type | Coverage (m² per litre) | Notes |
|---|---|---|
| Standard emulsion | 10 m²/L | Most common for interior walls. |
| Durable/mid‑sheen emulsion | 12 m²/L | Great for kitchens, hallways, and busy areas. |
| Ceiling paint | 11 m²/L | Thicker formula for smoother overhead coverage. |
| Primer/undercoat | 8 m²/L | Ideal for bare or porous surfaces that absorb more paint. |
How Paint Coverage Is Calculated
The paint coverage calculator handles the maths automatically, but the basic calculation is straightforward:
Paintable area × number of coats ÷ paint coverage per litre = litres of paint required
For a full room, calculate the wall area using:
(Length + Width) × 2 × Height
Subtract any doors and windows, then add the ceiling area if you’re painting it:
Length × Width
Most rooms need two coats, although fresh plaster, porous surfaces or major colour changes may require more. Finally, divide the total area by the coverage rate of your chosen paint.
Example
For a 4m × 3m room with 2.4m-high walls:
- Wall area: 33.6 m²
- Minus one door and one window: 30.2 m²
- Two coats: 60.4 m²
- At 10 m² per litre: about 6 litres of paint
The calculator does this instantly using your own room measurements, making it easier to estimate how much paint you need accurately.
How Many Litres of Paint Do I Need?
The amount of paint you need depends on the size of the area, the number of coats and the paint’s coverage rate. As a rough guide, a 4m × 3m bedroom with 2.4m-high walls needs around 6 litres of standard emulsion for two coats, after allowing for a typical door and window.
For an accurate estimate, enter your own room measurements into the paint coverage calculator above.
Before You Buy Your Paint
A few practical checks can help you get a better result and avoid running short:
- Allow for two coats on most walls. Dark colours, fresh plaster or major colour changes may need an extra coat.
- Prime bare or porous surfaces before applying your topcoat, as they can absorb significantly more paint.
- Mix multiple tins together if you need more than one tin of the same colour, helping to keep the finish consistent.
- Use the right roller for the surface — short pile for smooth walls, medium pile for light texture and long pile for rougher finishes.
- Check drying times on the paint before applying another coat.
It is also worth keeping a small amount of leftover paint for future touch-ups. See our full guide on How to Prepare Your Home for Professional Painting for more information.
FAQs
It depends on the room size, number of doors and windows, number of coats and the paint’s coverage rate. As a rough guide, a typical 4m × 3m bedroom with 2.4m-high walls may need around 6 litres of emulsion for two coats. For a more accurate figure, use the paint coverage calculator with your actual measurements.
Most interior paints cover around 8–12 m² per litre, although this varies between products, finishes and surfaces. Always check the manufacturer’s stated coverage before buying, particularly when painting porous or textured walls.
In most cases, yes. Two coats usually give the most even colour and finish. Fresh plaster, porous surfaces, dark colours or a significant colour change may require additional preparation or another coat.
Fresh plaster can absorb considerably more paint than an already painted wall. It normally needs an appropriate mist coat or primer first, followed by the required topcoats. This seals the surface and helps the finish coat cover more evenly.
