How to Estimate Paint for Any Room
Calculating paint quantities starts with measuring the total wall area of your room. Multiply the perimeter (the sum of all wall lengths) by the ceiling height to get the gross wall area in square metres. From there, subtract the area of any doors and windows, since these surfaces will not be painted. A standard internal door is roughly 1.8 square metres, while a typical window opening is about 1.5 square metres.
Once you have the net paintable area, multiply it by the number of coats you plan to apply. Most walls need two coats for an even, professional-looking finish, though you may need three if you are covering a dark colour with a lighter shade. Divide the total area by the coverage rate printed on your paint tin, usually between 10 and 14 square metres per litre for standard emulsion.
Choosing the Right Paint for Your Project
The type of paint you choose affects both coverage and durability. Matt emulsion is the most popular finish for living rooms and bedrooms, offering a flat, non-reflective look that hides minor wall imperfections. Silk and satin emulsions have a slight sheen and are easier to wipe clean, making them a good choice for hallways, kitchens and children’s rooms. For woodwork such as skirting boards, door frames and window sills, a dedicated wood paint in gloss or eggshell finish provides the hard-wearing surface needed in high-traffic areas.
If you are painting new plaster, always apply a mist coat first. This is simply standard emulsion thinned with about 10 per cent water, which allows the paint to soak into the porous surface and create a stable base for subsequent coats. Skipping this step often leads to peeling and flaking later on. For detailed product guidance, always check the coverage information on your chosen paint tin or ask at your local DIY store.
Tips for Getting a Professional Finish
Preparation accounts for the majority of the work in any painting project. Fill cracks and holes with a suitable filler, sand the surface smooth once dry, and wipe down walls with a damp cloth to remove dust. Mask off edges with painter’s tape for clean, straight lines around ceilings, door frames and light switches. Use a small brush to cut in around the edges before rolling the main wall area. Always work from top to bottom and maintain a wet edge to avoid visible lap marks.
You can explore our wallpaper calculator if you are considering wallpaper instead, or use the room area calculator to measure rooms with irregular shapes. For official guidance on making your home more energy efficient while you renovate, see the GOV.UK energy efficiency page.
This calculator provides estimates for guidance only. Results are based on the figures you enter and assume standard door (1.8 m²) and window (1.5 m²) sizes. Actual paint requirements may vary depending on surface condition, paint brand and application method. This is not professional decorating advice. For specific product guidance, check the coverage information on your chosen paint tin.