Calculate exactly how much paint you need for a room, apartment or building using formulas, tables and real examples. Never buy too much or too little.
Underbuying causes project delays and batch-mismatch color risk. Overbuying creates storage concerns and unnecessary cost. The key is accurate m² measurement and the product's theoretical coverage value.
Walls:
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Area (m²) = Perimeter (m) × Height (m) − Door/Window Areas
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Subtract ~2 m² for a door, ~1–1.5 m² for each window.
Ceiling: Length × Width
Example: Room 4×5 m, 2.8 m ceiling, 1 door + 2 windows:
Walls: 2×(4+5)×2.8 − 2 − 2.4 = 46 m² · Ceiling: 20 m² · Total: 66 m²
| Product Type | Theoretical | Practical | Coats |
|---|---|---|---|
| Interior water-based matt | 12–16 m²/L | 9–12 m²/L | 2 |
| Interior high-gloss | 10–14 m²/L | 8–11 m²/L | 2 |
| Exterior acrylic | 8–12 m²/L | 6–9 m²/L | 2 |
| Alkyd enamel | 12–16 m²/L | 9–12 m²/L | 2 |
| Anti-rust primer | 6–10 m²/L | 5–8 m²/L | 1–2 |
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Paint (L) = Area (m²) × Coats ÷ Practical Coverage (m²/L)
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Example: 66 × 2 ÷ 10 = 13.2 L → Buy 15 L (+10% buffer)
| Surface Condition | Extra Consumption |
|---|---|
| New plaster, smooth | Base value |
| Old painted, smooth | +5–10% |
| Rough textured plaster | +20–30% |
| Porous concrete | +30–50% |
Does color change require more paint?
Dark to light: up to 3 coats. A filler primer reduces this significantly.
Why is batch number important?
Even the same color code may have slight tone variation between batches. Buy all you need from one order for large projects.
What is the shelf life of leftover paint?
Open water-based: 6–12 months; sealed: 2–3 years. Solvent sealed: 3–5 years.
Does using primer reduce total paint needed?
Yes — the right primer can cut topcoat consumption by 20–30%, usually reducing total cost.
