There's a particular DIY frustration that arrives when you open your last tin of paint and stare at three-quarters of an unpainted wall. Or the opposite: stacking four leftover tins in the shed where they'll slowly turn unusable. Both are caused by one thing — not calculating paint quantities properly before starting.
Coverage Rate: The Key Number
Every paint tin states its coverage rate in m² per litre. Common rates: matt/silk emulsion 10-12 m²/litre | gloss/satinwood 13-17 m²/litre | primer 10-14 m²/litre | masonry paint 4-8 m²/litre. Our paint calculator applies these rates automatically. Use our area calculator for room dimensions first.
Step 1: Calculate Wall Area
Perimeter × ceiling height, minus doors (≈3.6 m²) and windows (≈1.44 m² each). Example: 5m × 4m room, 2.4m ceiling, one door, one window: (5+4+5+4) × 2.4 − 3.6 − 1.44 = 38.16 m².
Step 2: Number of Coats
- Bare/new plaster: mist coat + 2 full coats
- Previously painted, similar colour: 2 coats
- Major colour change: 2-3 coats
Multiply wall area by coats: 38.16 m² × 2 = 76.32 m² total coverage required.
Step 3: Litres Needed
76.32 ÷ 12 m²/litre = 6.36 litres. Round up to available tin sizes (1L, 2.5L, 5L, 10L). A 5L + 2.5L = 7.5L is practical here. Add 10% for wastage and touch-ups.
Don't Forget the Ceiling
Ceiling area = length × width. 5 × 4 = 20 m². At 12 m²/litre over 2 coats: 40 ÷ 12 = 3.33 litres. One 5L tin of white emulsion covers this with overage for touch-ups.
Keep a Touch-Up Tin
Always keep a small sealed tin for future touch-ups. Properly stored paint lasts 2-5 years and makes scuffed skirting disappear in seconds. It's worth far more than its cost when you need it two years after the job is done.
Further reading: Dulux's website has detailed per-product coverage guidance. Use Dulux's paint quantity guidance.