Paint Coverage Calculator for Wall Area & Litres
Calculate exact paint quantities for any room — enter your room, door and window dimensions to get a precise volume and tin-count specification, including surface condition and coat allowances.
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Paint Specification
How to Use This Paint Calculator
- Choose Metric or Imperial to set your working units.
- Enter your room length, width and height, or switch to entering the total wall area directly for an irregular room.
- Enter the height, width and count of doors and windows, so they can be deducted from the wall area.
- Choose a paint type or enter a custom coverage rate, and set the number of coats and surface condition.
- Click Calculate for your total paint volume and a suggested tin-size purchase.
Understanding Coverage Rate, Coats and Surface Condition
Coverage rate is how much area a litre of paint covers, printed on the tin as m² per litre — it varies by paint type, with matt emulsion typically covering more per litre than eggshell, gloss or masonry paint. Always use the figure on your actual tin over a general estimate where possible.
Number of coats directly multiplies the paint needed — two coats is the practical minimum for even, opaque coverage on most walls, though a significant colour change or new plaster may need a third.
Surface condition accounts for porosity. A previously painted, sealed wall needs no extra allowance, but new plaster can need around 20% more paint, and a first-time paint job needing priming can need up to 30% more, since bare or porous surfaces absorb more paint than a sealed one.
Worked Example: A Standard Bedroom
Take a 500cm × 400cm room with a 270cm ceiling height, one standard door (200cm × 80cm) and one window (120cm × 120cm). The gross wall area comes to 48.6m², reducing to 45.56m² once the door and window are deducted. At 2 coats with a matt emulsion covering 14m² per litre, and no surface allowance, that comes to just over 6.5 litres of paint — comfortably covered by a 5L tin plus a smaller top-up.
Frequently Asked Questions
How much paint do I need for a room?
It depends on the wall area, minus doors and windows, the paint's coverage rate, the number of coats, and the surface condition. Use the calculator above with your own measurements for an exact volume and tin-size recommendation.
What is paint coverage rate?
Coverage rate is how much area a litre of paint covers, usually printed on the tin as m² per litre. It varies by paint type — matt emulsion typically covers around 14m² per litre, eggshell and gloss around 12m², and masonry paint around 10m².
Do I need to deduct doors and windows from the wall area?
Yes, for an accurate quantity. Doors and windows don't get painted with wall paint, so their combined area should be subtracted from the total wall area before calculating how much paint is needed.
How many coats of paint do I need?
Two coats is the practical minimum for most walls, giving even, opaque coverage. New plaster, a significant colour change, or a porous surface may need a third coat or a dedicated primer first.
What is a surface condition allowance for paint?
It's extra paint accounted for beyond the standard coverage rate, to reflect how porous or absorbent a surface is. New plaster typically needs around 20% more paint, and a first-time paint job needing priming can need up to 30% more, since bare or porous surfaces soak up more paint than a previously painted, sealed wall.