How to use the Paint Quantity Calculator for Walls
- 1. Enter the roomLength, width and height in metres or feet, and whether to paint the ceiling.
- 2. Deduct openingsNumber and size of doors and windows. Add coats and coverage from the can.
- 3. Get the quantityLitres of paint and primer, putty, pack sizes and cost at your price.
How paint quantity is estimated
Wall area = 2 × (length + width) × height. Add the ceiling (length × width) if needed, then deduct doors and windows. Paint (litres) = net area × number of coats ÷ coverage per litre, plus a small wastage allowance.
Coverage depends on the product and wall. Many emulsion cans state about 9–12 m² per litre per coat (about 100–130 ft²), but always read the label of the paint you buy. Primer is usually one coat. Putty consumption is given on the bag in kg per m².
Worked example and site tips
A room 4 × 3.5 m with 3 m height and the ceiling painted: walls 45 m² + ceiling 14 m² − one door 1.89 m² − two windows 2.88 m² = 54.23 m². Two coats at 10 m²/L with 5% wastage = 54.23 × 2/10 × 1.05 = 11.4 litres, for example one 10 L and two 1 L packs.
- New plaster usually needs primer; a repaint in the same colour may not.
- Dark to light colour changes may need an extra coat.
- Buy all paint of one colour from the same batch.
Frequently asked questions
How much paint is needed for a 10 × 12 ft room?
With 10 ft walls and no ceiling, walls are 2 × (10 + 12) × 10 = 440 ft². Two coats at 100 ft² per litre need about 8.8 litres before deducting doors and windows.
Should I deduct doors and windows?
Yes, for a material estimate. Measurement rules for payment may differ, but for buying paint, deduct the openings.
What coverage should I use?
Use the coverage printed on the paint can. It changes with brand, product and wall texture, so the tool keeps it editable.
Is this calculator free?
Yes. You fill a short form once to see your result, and other Uncodemy tools then open without the form. Everything is calculated in your browser and nothing you type is uploaded.