Paint Calculator

Calculate how much paint you need for walls and ceilings. Automatically deducts doors and windows and shows the tin sizes to buy.

Buying too much paint wastes money; buying too little means a second trip to the store and potential colour-matching headaches. This tool takes the guesswork out by calculating the exact coverage area, deducting doors and windows, and telling you which tin sizes to buy for the most economical purchase.

Coverage rates vary by paint type. Most emulsions cover 12 to 14 square metres per litre on smooth surfaces, but textured walls, bare plaster, and dark-to-light colour changes can reduce that significantly. Two coats are standard for walls; ceilings usually need two as well if the previous colour differs.

The British Coatings Federation reports that UK households buy over 360 million litres of decorative paint each year, with emulsion accounting for around 70% of volume (BCF). Calculating your requirement before you buy ensures you get exactly the right amount.

How this calculator works

  1. Enter the room dimensions — length, width, and ceiling height.
  2. Specify the number of doors, windows, and coats of paint required.
  3. The tool calculates the paintable area, total litres needed, and the most cost-effective combination of tin sizes.

Written by the CalcStack team · Last updated April 2026

Frequently asked questions

How much paint do I need per square metre?▾
Most emulsion paints cover approximately 10-14 m2 per litre per coat. The standard assumption is 12 m2/litre. Rough or textured surfaces absorb more paint and may only achieve 8-10 m2/litre.
How many coats of paint do I need?▾
Two coats is standard for a good finish. You may need three coats if painting a dark colour over light, or vice versa. One coat may suffice for a quick refresh with the same colour.
What is the coverage rate on the tin?▾
Manufacturers state coverage on the tin (e.g., 12 m2/litre). This assumes a smooth, sealed surface with a roller. Actual coverage varies with surface texture, paint type, and application method.
Should I paint the ceiling too?▾
Painting the ceiling refreshes the whole room. Use a matt white ceiling paint (which hides imperfections) applied with a roller on an extension pole. Budget separately from wall paint.
How do I calculate wall area for an L-shaped room?▾
Break the room into two rectangles and calculate each separately. Measure the perimeter of the room and multiply by ceiling height for wall area, then deduct openings.
What size paint tins should I buy?▾
Paint comes in 1L, 2.5L, and 5L tins typically. For small rooms (under 20m2 wall area), 2.5L tins work well. For larger rooms, 5L tins are more economical. Buy 1L for touch-ups or accent walls.
Do I need primer?▾
Use primer on new plaster, bare wood, or when making a dramatic colour change. Modern one-coat paints include primer but true primer gives a better base. Allow primer coverage of about 10 m2/litre.
How do I paint around doors and windows?▾
Use a small brush or mini roller to cut in around edges. Our calculator deducts standard door (1.9m2) and window (1.5m2) areas. Measure your actual openings for greater accuracy.
What paint finish should I use?▾
Matt for ceilings and low-traffic walls. Eggshell or silk for living areas (slightly wipeable). Satin or semi-gloss for kitchens, bathrooms, and woodwork (moisture-resistant and wipeable).
How long does paint take to dry?▾
Emulsion: touch dry in 1-2 hours, recoat after 4 hours. Gloss/eggshell: touch dry in 4-6 hours, recoat after 16 hours. Allow longer in cold or humid conditions. Good ventilation speeds drying.

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© 2026 CalcStack — a Flavoureak UK Ltd product. Coverage assumes smooth surfaces. Check your paint tin for specific coverage rates.