About This Calculator
This calculator helps you determine the amount of paint required for your room. It accounts for room dimensions, automatically deducts standard door and window sizes, and adjusts for surface condition (new plaster absorbs more paint).
Different paint types have different coverage rates - masonry paint covers less area per litre than emulsion due to the rough surface texture.
How to Use
- Measure your room (length × width × wall height)
- Count doors and windows (standard sizes are deducted)
- Choose paint type (emulsion, masonry, wood, primer)
- Select surface condition (new plaster needs more paint)
- Decide on number of coats (2 typical for good coverage)
- Calculate quantity
Paint Coverage Rates
| Paint Type | Coverage (m²/litre) | Typical Use |
|---|---|---|
| Emulsion | ~12 m²/litre | Walls and ceilings |
| Masonry | ~5 m²/litre | Exterior walls |
| Wood/Trim | ~10 m²/litre | Skirting, doors, frames |
| Primer | ~10 m²/litre | New plaster, bare surfaces |
Surface Condition Factors
Good Condition
Previously painted, smooth
Standard coverage rate
Poor Condition
Flaking, porous, stained
+25% more paint needed
New Plaster
Unpainted, very absorbent
+40% more paint needed
Standard Deductions
The calculator automatically deducts these standard sizes:
- Door: 2.0 m² (approximately 2m × 1m)
- Window: 1.5 m² (approximately 1.2m × 1.25m)
Painting Tips
- Always apply at least 2 coats for even colour and durability
- New plaster must be sealed with a mist coat (diluted emulsion) first
- Buy all paint from the same batch for colour consistency
- Keep leftover paint for future touch-ups
- Darker colours may need 3 coats for full coverage
- Calculate for ceilings separately if using different paint
Ready to Calculate?
Enter your room dimensions and paint specifications to get accurate quantities.
Launch CalculatorUKUK Building Regulations
References & Sources
Standards Cited
- BS 6150 — Painting of buildings — Code of practice
Defines standard coverage rates, surface preparation requirements, and number of coats guidance
Formulas Used
- Wall area:
wallArea = 2 x (roomLength + roomWidth) x wallHeight
Source: Basic geometry (room perimeter x height) - Net wall area:
netWallArea = wallArea - (numDoors x 2.0) - (numWindows x 1.5)
Source: BS 6150 — Standard door deduction: 2.0 m2, standard window deduction: 1.5 m2 - Effective coverage:
coveragePerLitre = baseCoverage x surfaceFactor
Source: BS 6150 / manufacturer data (Dulux, Crown) — Surface factors: good condition 1.0, poor condition 0.8, new plaster 0.7 - Total litres:
totalLitres = (totalArea / coveragePerLitre) x numberOfCoats
Source: BS 6150 - Cans needed:
cansNeeded = ceil(totalLitres / 5)
Source: Standard 5L can size
Key Assumptions
- Base coverage rates: emulsion 12 m2/L, masonry 5 m2/L, wood/trim 10 m2/L, primer 10 m2/L — BS 6150 / Dulux and Crown manufacturer guidelines
- Surface condition factors: good (previously painted) 1.0, poor 0.8, new plaster/porous 0.7 — BS 6150
- Standard door area deduction: 2.0 m2 (approx 2m x 1m) — Industry standard practice
- Standard window area deduction: 1.5 m2 (approx 1.2m x 1.25m) — Industry standard practice
- Standard can size: 5 litres — Dulux / Crown standard product sizes