Calculator Form
Use the responsive grid below. Large screens show three columns, smaller screens show two, and mobile shows one.
Example Data Table
| Scenario | Net Area | Coats | Coverage Rate | Waste | Estimated Litres |
|---|---|---|---|---|---|
| Small interior wall | 24 m² | 2 | 5 m²/L | 8% | 10.37 L |
| Medium room perimeter | 52 m² | 2 | 4.8 m²/L | 10% | 23.83 L |
| Porous exterior façade | 90 m² | 3 | 4.5 m²/L | 12% | 74.67 L |
Formula Used
The calculator estimates limewash volume from surface size, coverage rate, coats, absorption, and waste.
Gross Area = Length × Height × Number of Walls
Net Area = Gross Area − Openings Area
Effective Coated Area = Net Area × Coats × Absorption Factor
Base Litres = Effective Coated Area ÷ Coverage Rate
Waste Litres = Base Litres × Waste Percentage
Total Litres Needed = Base Litres + Waste Litres
Containers Needed = Ceiling(Total Litres Needed ÷ Container Size)
Rounded Purchase Cost = Containers Needed × Container Size × Price Per Litre
Higher absorption factors represent rougher or thirstier substrates. Smooth walls need less material. Historic, chalky, or porous walls usually need more.
How to Use This Calculator
- Choose metric or imperial units.
- Enter wall length, height, and total number of walls.
- Add total openings area for doors, windows, and excluded spaces.
- Enter the product coverage rate and number of coats.
- Select a surface profile or type your own absorption factor.
- Set waste allowance, container size, and price per litre.
- Press calculate to view litres, containers, costs, CSV export, PDF export, and the graph.
FAQs
1. What does limewash coverage mean?
Limewash coverage is the surface area one litre can coat under specific conditions. It changes with porosity, dilution, number of coats, and application method. This calculator turns those variables into a practical material estimate.
2. Why do rough walls need more limewash?
Rough or porous walls absorb more liquid and create more texture area. That means each litre spreads less efficiently. Using an absorption factor helps you avoid underestimating material on rendered, chalky, or older substrates.
3. Should I subtract windows and doors?
Yes. Large windows, doors, vents, and other uncoated areas should be removed from the total. That gives a more realistic net area and reduces unnecessary purchasing.
4. How many coats are normal for limewash?
Many limewash projects use two coats, but porous masonry or stronger color depth may need three or more. Always check the product instructions and test a small section before full application.
5. What waste percentage should I use?
For careful indoor work, 5% to 10% is common. For porous walls, touch-ups, or challenging exteriors, 10% to 15% is safer. Higher waste allowances reduce the risk of running short mid-project.
6. Does this calculator work for imperial units?
Yes. Switch the unit system to imperial and enter dimensions in feet and area values in square feet. The calculator converts values internally and still reports litres for material purchasing.
7. Why are container costs different from exact liquid costs?
Exact liquid cost uses only the calculated litres. Purchase cost uses whole containers because suppliers sell fixed pack sizes. The rounded purchase figure is usually the more realistic budgeting number.
8. Can I use this for interior and exterior walls?
Yes. The method works for both. Exterior surfaces usually need higher waste allowances and sometimes higher absorption factors because texture, weathering, and patch variation can increase limewash demand.