Bathroom Waterproofing Calculator
Floor, walls and detail strips, with coating and membrane quantities.
Quick answer
With the default inputs: Room length 2.0 m · Room width 1.8 m · Wall upturn height 1.8 m etc.Total waterproofing area 15.84 m²
Edit the inputs below to recalculate.Inputs
Result
Total waterproofing area
15.84m²
| Floor area | 3.60m² |
| Floor perimeter | 7.60m |
| Wall area | 12.24m² |
| Wall run after deducting door | 6.80m |
| Detail strips | 2.28m² |
| Coating required | 31.7kg |
| Drums at 20 kg | 2cans |
| Membrane with waste | 18.2m² |
| Area per m² of floor | 4.40× |
Wall area = (floor perimeter − door width) × upturn height; the doorway has no upturn, so deducting it is mandatory or you overcount by 5-10%. Code upturn heights: at least 1.8 m in showers, 0.75 m beside baths and squat pans, 0.3 m on other walls, 1.2 m at washbasins. Corners, pipe penetrations and drains take 300 mm wide detail strips, listed separately here. Finish with a 24-hour ponding test at least 20 mm deep.
Formula
| Floor area | A = length × width |
| Wall run | L = 2 × (length + width) − door width |
| Wall area | A = L × upturn height |
| Total area | A = floor + wall |
| Coating | G = A × coverage |
| Membrane | A = total × (1 + waste) |
A 2.0×1.8 m bathroom with 1.8 m upturn, 0.8 m door and 2.0 kg/m²: 3.6 m² floor, 12.24 m² walls, 15.84 m² total, 31.7 kg coating, 18.2 m² membrane and 2.28 m² of detail strips.
FAQ
How high should wall waterproofing go?
Under the residential interior waterproofing code: at least 1.8 m in showers and no lower than the shower head; 0.75 m beside baths and squat pans; 1.2 m at basins; 0.3 m elsewhere. Lightweight partitions (AAC, steel stud) need the full wall to full height because they wick water. This is the most complained-about leak location — do not cut it to 0.3 m to save material.
Coating or membrane?
Floors suit liquid coating: it forms a seamless film that copes with pipe penetrations, drains and corners, and is easy to apply in tight rooms. Membrane has laps, which fail in confined and detailed areas — it belongs on large roofs and basement walls. A coating-plus-membrane build-up is more expensive but reliable. If walls are tiled, choose a coating compatible with tile adhesive or the tiles will debond.
How is the ponding test done?
Once the membrane has fully cured — about 48 hours for coatings — plug the drain and doorway, pond at least 20 mm deep for 24 hours, then inspect the ceiling below for leaks and check that the level has not dropped appreciably. No leak and no drop means pass. Any failure must be repaired and retested, and a second test is done after finishing. Both need photo records and signatures.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.