Paint Quantity Calculator

The paint calculator turns a room geometry into a shopping list. Wall area is computed as room length × wall height × number of walls, minus the standard openings (each door ≈ 2 m², each window ≈ 1.5 m²). The painted surface scales with the number of coats — most jobs need two for proper coverage. Dividing by the manufacturer-published coverage rate (m² per litre, usually 10–12 for top-coat emulsion) gives litres; adding wastage and rounding up to whole buckets gives the order. A separate primer estimate uses the ~12 m² per litre rate that primer manufacturers print on the can.

Core formula

Net paintable area scales with the number of coats and divides by coverage. Buckets always round up.

Paintable Area = L × H × Walls − Doors×2 − Windows×1.5 | Litres = (Paintable × Coats ÷ Coverage) × (1 + Wastage%) | Buckets = ⌈Litres ÷ Bucket Size⌉

Worked example — 5 × 3 m room with 4 walls and 2 windows

Inputs: room length = 5 m, wall height = 3 m, walls = 4, doors = 1, windows = 2, coats = 2, coverage = 10 m²/L, wastage = 5%, bucket = 20 L.

1. Raw wall area = 5 × 3 × 4 = 60 m²
2. Openings = 1 × 2 + 2 × 1.5 = 5 m²
3. Paintable area = 60 − 5 = 55 m²
4. Surface to cover = 55 × 2 coats = 110 m²
5. Litres exact = 110 / 10 = 11 L; with 5% wastage = 11.55 L
6. Buckets = ⌈11.55 / 20⌉ = 1 bucket of 20 L
7. Primer = 55 / 12 ≈ 4.6 L

Common mistakes to avoid

• Forgetting the second coat — 80% of failures trace back to a single-coat job.
• Ignoring the coverage rate on the can — premium paints can cover 12 m²/L; budget paints drop to 7 m²/L.
• Skipping primer on raw plaster — the top coat absorbs unevenly and you end up needing more, not less.
• Using a single number for all walls — feature walls with dark colours often need three coats.

Tips for accurate estimates

• Always buy one extra litre per ~50 m² for touch-ups after furniture moves in.
• Use the 20 L bucket for large jobs — the per-litre price is much lower than gallons.
• Saudi market top brands (Jazirah, Sipes, Caparol) publish coverage rates of 10–12 m²/L for emulsions.
• Dark colours over light walls always need three coats; budget accordingly.