Waterproofing calculator for roofs, bathrooms and tanks
This waterproofing calculator works out the area to treat and the material you need: litres of liquid membrane, kilograms of cementitious or crystalline coating, or square metres and rolls of bituminous membrane. Choose a roof, bathroom, basement or water tank, enter its size, pick a system, and it applies the consumption per coat, the number of coats and an allowance for wastage and laps.
Add prices and a labour rate to turn it into a waterproofing cost calculator — total cost, cost per m² and per square foot. The presets come from item analyses in CPWD’s Delhi Analysis of Rates 2023, so every default can be traced; your own product’s datasheet should always win, and every field can be changed.
How to use the Waterproofing Calculator
- Choose metres or feet and where the waterproofing goes: roof, bathroom, basement or tank, or type a known area.
- Enter length and width, the upturn height on parapets or walls (or the tank depth), how many identical areas there are, and any deduction or extra shower-wall area.
- Pick a waterproofing system. Its materials, consumption, coats, wastage, pack size and an example price appear below.
- Change the consumption and coats to match your product datasheet, enter today’s prices and labour rate, and any GST or overhead percentage.
- Read the quantities, packs and cost, and copy the estimate.
Waterproofing Calculator features
Area with upturns
Roof plus parapet upturn, bathroom floor plus wall height and shower walls, tank walls plus floor.
Five systems
Elastomeric liquid membrane, flexible cementitious coating, crystalline slurry for walls or floors, and two-layer APP membrane.
Datasheet-ready
Consumption per m² per coat, coats or layers, wastage, pack size and price for every material.
Packs and rolls
Rounds up to whole buckets, bags or 10 m² membrane rolls.
Cost per sq ft
Materials, labour and GST or overheads, with cost per m² and per square foot.
How waterproofing quantity is calculated
Quantity = area × consumption per coat × number of coats × (1 + wastage). For a roof the area is L × W plus the upturn on the parapets, 2 × (L + W) × upturn height. Worked example: a 10 × 8 m terrace with a 300 mm upturn has 80 + 36 × 0.3 = 90.8 m². An elastomeric membrane at 10.76 litres per 10 m² for three coats, plus 5% wastage, needs 90.8 × 1.076 × 1.05 ≈ 102.6 litres — six 20-litre buckets.
For a bathroom, treat the floor and the walls up to 300 mm or more, and shower walls higher. Two 2.4 × 1.8 m bathrooms with a 300 mm upturn and 3 m² of shower wall each need (4.32 + 2.52 + 3) × 2 = 19.68 m².
Preset consumption (CPWD DAR 2023)
Example prices are the basic Delhi rates in that analysis (April 2023, before GST and contractor’s overheads): ₹255 per litre of elastomeric membrane, ₹170 per kg of cementitious coating, ₹214 per kg of crystalline slurry, ₹90 per m² of APP felt. Prices change; enter current ones.
| System | Consumption | Labour in the analysis |
|---|---|---|
| Elastomeric liquid membrane on roof (22.22A) | 10.76 L per 10 m², three coats, + 5% | coolie 0.67 + painter 0.67 day per 10 m² |
| Flexible cementitious coating (22.23A) | 14.35 kg per 10 m², three coats, + 5% | coolie 0.23 + painter 0.46 day per 10 m² |
| Crystalline slurry, vertical (22.23.1) | 0.70 kg/m² per coat, two coats | lump sum |
| Crystalline slurry, horizontal (22.23.2) | 1.10 kg/m², one coat | lump sum |
| APP membrane, two layers (14.86) | 2 × area + 10%; primer 0.40 L/m²; bitumen 1.20 kg/m² × 3 | painter 2.16, beldar 3.24, mistry 0.18 day per 30 m² |
Getting a reliable estimate
- Use the coverage on the product’s technical data sheet; coverage varies with the brand, surface roughness and the dry film thickness required.
- If the sheet gives coverage in m² per litre, enter 1 ÷ coverage as the quantity per m² (8 m²/L per coat = 0.125 L/m²).
- Allow for falls and screeds: the plaster calculator estimates cement-sand screed, and the roofing calculator handles pitched roofs.
- Price the labour separately if your applicator works by the day: the labour cost calculator includes liquid waterproofing norms.
Waterproofing Calculator FAQ
How do I calculate waterproofing area for a terrace?
Multiply length by width and add the parapet upturn: 2 × (length + width) × upturn height. A 30 × 40 ft terrace with a 1 ft upturn is 1,200 + 140 = 1,340 sq ft.
How much waterproofing material per square foot?
It depends on the product. The elastomeric preset uses about 0.1 litre per sq ft for three coats; the cementitious preset about 0.14 kg per sq ft for three coats. Check the datasheet.
What is roof waterproofing cost per sq ft?
Material plus labour divided by area. With the preset 2023 Delhi rates the elastomeric system works out to roughly ₹36 per sq ft before GST and overheads; enter current local prices for a real figure.
How many rolls of APP membrane do I need?
Two-layer work needs about 2 × area + 10% for laps. 90.8 m² of roof needs 199.8 m² of membrane, or 20 rolls of 10 m².
How high should bathroom waterproofing go on the walls?
Many specifications take it 300 mm up the walls, and higher — often to full height — in the shower zone. Follow your architect’s or product specification.
Is this a quote?
No. It is an estimate from the coverage and prices you enter. Get a site inspection for cracks, slopes and drainage before ordering.