Paint Quantity Calculator
Find how many litres of paint and how many coats you need for a room or house, plus primer and total cost.
Inputs
Emulsion covers 110–140 sq ft per litre per coat
Formula
- Wall area = 2 × (L + W) × H − openings
- Paint area = wall area (+ ceiling area) × coats
- Litres = paint area ÷ coverage per litre
Paint is sold by coverage: one litre of emulsion covers roughly 120 sq ft in a single coat on a smooth, primed wall. Measure the four walls, subtract doors and windows, multiply by the number of coats and divide by coverage. Fresh plaster drinks more paint, so a primer coat is added separately.
Step-by-step calculation
- 1
Wall area
2 × (L + W) × H − openings
400 sq ft
- 2
Total area
walls + ceiling
520 sq ft
- 3
Litres
area × coats ÷ coverage
8.67 L
Worked example
- 1A 12 × 10 ft room with 10 ft walls: 2 × (12+10) × 10 = 440 sq ft.
- 2Minus 40 sq ft of openings = 400 sq ft; ceiling adds 120 sq ft.
- 3Two coats over 520 sq ft = 1,040 sq ft ÷ 120 ≈ 8.7 litres.
Tips
- Always prime new plaster — it saves almost a full coat of expensive emulsion.
- Buy paint in the largest pack you need; 20 litre buckets cost far less per litre than 1 litre tins.
Frequently asked questions
How much paint for a 10×10 room?
About 6–7 litres for two coats on the walls, plus 1 litre for the ceiling.
How many coats do I need?
Two coats over primer for a new wall; one coat is often enough when repainting the same shade.
Does texture change the quantity?
Yes — rough or textured surfaces reduce coverage by 20–30%, so lower the coverage figure.
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