Everyday Life⏱ 5 min read
How to Calculate Paint Coverage for Any Room (With Worked Examples)
Paint tins list coverage in m² per litre — but working out how many litres you need requires knowing your wall area, the number of coats, and how to account for doors and windows.
Buying too little paint means a second trip to the shop mid-job — and a potential batch mismatch if the colour isn't mixed consistently. Buying too much wastes money. Here's the exact calculation for any room.
Step 1: Calculate Wall Area
Wall area = Perimeter × Height
Perimeter = 2 × (Length + Width) for rectangular rooms
Example: 4m × 3.5m room, 2.4m ceiling height
Perimeter = 2 × (4 + 3.5) = 15m
Wall area = 15 × 2.4 = 36 m²
Step 2: Deduct Doors and Windows
Standard door: 0.9m × 2.0m = 1.8 m²
Standard window: 1.2m × 1.0m = 1.2 m²
Large window: 1.8m × 1.2m = 2.16 m²
Example room: 2 windows and 1 door
Deductions: (2 × 1.2) + 1.8 = 4.2 m²
Net paintable wall area: 36 − 4.2 = 31.8 m²
Step 3: Apply Coverage Rate
Litres needed per coat = Area ÷ Coverage (m²/litre)
Coverage rates vary by product quality:
Budget paint: 8–10 m²/litre
Mid-range: 12–14 m²/litre
Premium / one coat: 14–16 m²/litre
Example: 31.8 m², mid-range paint (12 m²/litre)
Litres per coat: 31.8 ÷ 12 = 2.65 litres
Two coats: 2.65 × 2 = 5.3 litres → buy 6 litres (or 2×2.5L tins)
Coverage by Surface Type
SurfaceWhy Coverage VariesAdjustment
New plasterVery absorbent — soaks up paintUse diluted mist coat first, add 20% extra
Painted walls (same colour)Standard absorbencyUse quoted coverage
Painted walls (colour change)May need 3 coats going lighterAdd one extra coat's worth
Bare brick or rough renderHighly textured, more surface areaReduce coverage by 25–30%
Woodchip / textured wallpaperHighly texturedReduce coverage by 20%
Ceiling Calculation
Ceiling area = Room length × Room width
= 4 × 3.5 = 14 m²
Ceiling paint coverage: typically 12–14 m²/litre
One coat: 14 ÷ 13 = 1.08 litres
Two coats (new plaster or colour change): 2.16 litres → buy 2.5L
Woodwork: Skirting, Door Frames, Windows
Skirting boards: measure total length in metres
Coverage for gloss/satinwood: typically 16–20 m² per litre
For 15m of skirting (0.1m tall):
Area = 15 × 0.1 = 1.5 m²
Two coats at 17 m²/litre: 3 ÷ 17 = 0.18 litres
→ 250ml sample pot is usually sufficient for a standard room
Always Buy Slightly More
Add 10% to all calculations for touch-ups, spills, and future repairs. Paint stored in sealed tins remains usable for 2–5 years. Having leftover matching paint for touch-ups is significantly more valuable than the small cost of the extra tin.