Liquid membrane Calculator: measuring notes and method
Measure returns as well as the floor
Add the specified wall areas, upstands and other coated faces. A floor footprint alone cannot represent the full waterproofing surface.
Use the correct application rate
Check whether the product’s published rate is per coat or for the complete system. Applying a full-system consumption rate once per coat would overcount material.
CHECK A PRACTICAL EXAMPLE
Per-coat coverage and system coverage differ
The illustration uses 12 m² and a hypothetical 1.5 m²/L rate, in 15 L containers.
Rate for one complete system
- Membrane required
- 8 L
- Containers to buy
- 1
Same rate applied twice
- Membrane required
- 16 L
- Containers to buy
- 2
These represent different interpretations of a label, not two valid choices for the same specification. If a rate already covers the complete system, use one coverage application; if it is per coat, enter the required number of coats. Verify with the product instructions.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Coating = (area − excluded area) × coats ÷ coverage per coat × (1 + waste ÷ 100). Containers are rounded up.
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Total surface area
- 24 m²
- Openings / excluded area
- 0 m²
- Number of coats
- 2 coats
- Coverage per coat
- 1.5 m²/L
- Container size
- 4 L
- Waste allowance
- 5 %
Membrane required: 33.6 L
Imperial worked example
- Total surface area
- 258.3339 ft²
- Openings / excluded area
- 0 ft²
- Number of coats
- 2 coats
- Coverage per coat
- 61.1188 ft²/US gal
- Container size
- 1.0567 US gal
- Waste allowance
- 5 %
Membrane required: 8.8762 US gal
Follow the calculation
- Net area = 24 − 0 = 24 m².
- Coat area = 24 × 2 = 48 m².
- Quantity = 48 ÷ 1.5 × 1.05 = 33.6 L. Divide by 4 L and round up for containers.
Unit conversions
Liquid conversions use US gallons (3.785411784 L), not UK imperial gallons (4.54609 L).
Reviewed 19 October 2026. How calculations are checked · Report a correction