TryBuildCalcBathroom Waterproofing Calculator Floor and wall band waterproofing estimator
Calculate waterproofing treatment area, material quantity, and cost for roofs, bathrooms, and basements.
🕒 Last updated: July 8, 2026
Inputs
Area Type
Bathroom / Wet Area Dimensions
ℹ️Height the waterproofing runs up every wall around the perimeter, commonly at least 300mm.
Treatment Material
ℹ️Two coats, applied perpendicular to each other, is the common default.
ℹ️Cementitious coatings typically cover 1.0-1.5 kg/m² per coat — confirm against the product data sheet.
Wastage
Primer
Cost
This bathroom / wet area waterproofing job covers approximately 7.70 m² (83 sq ft) of treatment area — you'll need about 25.4 kg of material (material quantity includes 10% wastage).
Area Type
Bathroom / Wet Area
Cementitious Coating
Treatment Area
7.70 m²
83 sq ft
Wastage Allowance
10%
Extra material for corners, joints & off-cuts
Material Required
25.4 kg
2 coats at 1.5 kg/m² each, incl. wastage
Bathroom / Wet Area Breakdown
Floor Area: 5.00 m² (54 sq ft)
Wall Band Area: 2.70 m² (29 sq ft)
Full-height shower wall not included in this estimate.
Wastage Impact on Material
Material Before Wastage: 23.1 kg
Extra Material From Wastage: 2.3 kg
Wastage sizes how much material to buy for detailing, joints, and off-cuts — the treated area itself (Treatment Area above) doesn't change.
Assumptions Used
Coverage rate: 1.5 kg/m² per coat | Coats: 2 | Wastage: 10%
Bill of Materials
Main material: 25.4 kg + recommended tools
+−
Bill of Materials
Main material: 25.4 kg + recommended tools
Computed items reflect your entered dimensions and material choice; consumables below are general recommendations — actual needs vary by product and site.
For Your Job
Cementitious Coating
25.4 kg
2 coats × 1.5 kg/m²
General Tools & Consumables
Chemical-resistant gloves
Masking tape / polythene sheeting
Corner fillet / coving compound
Mixing bucket/drum & stirrer
Wire brush
Stiff-bristle brush or broom
Pipe penetration sealant/collars
Flood-test damming material (sandbags or timber battens)
Primer
Approximate results for planning only. Verify with a professional.
Choosing between cementitious, liquid/PU, and sheet membrane? Waterproofing Methods Guide →
Comparing this against a below-slab damp proof membrane? Damp Proof Membrane (DPM) Guide →
Bathroom / Wet Area Waterproofing (Plan View)
Looking for the verification checklist, reference tables, or tips and mistakes?See the complete Waterproofing Calculator.
Bathroom floor and wall band estimate
This page is pre-filled for a common 2.5 m x 2 m bathroom with a 0.3 m wall band (no separate shower wall) — treatment area comes to 7.7 m² (5 m² floor plus 2.7 m² wall band), needing about 25.41 kg of cementitious coating at 2 coats and 10% wastage.
The 300mm wall band running around the bathroom's full perimeter is what most online waterproofing estimates skip — it accounts for over a third of this bathroom's total treatment area, not floor alone.
- Bathroom: 2.5 m x 2 m.
- Wall band: 0.3 m.
- No separate shower wall.
How Is Waterproofing Calculated?
Every mode follows the same overall sequence — calculate the treatment area for the chosen scenario, add wastage, then convert to material quantity (coating weight or membrane rolls), optional primer, and cost — but the area formula and material-quantity method differ by mode and material type.
Step 1 — Treatment Area (by Area Type)
Roof/Terrace = (Length × Width) + optional Parapet (Perimeter × Parapet Height)
Bathroom/Wet Area = (Floor Length × Width) + (Wall Perimeter × Wall Band Height) + optional Shower Wall (Width × (Height − Wall Band Height))
Basement/Retaining Wall = Wall Length × Wall Height
Multiple Sections = Sum of every section's area above, combined into one total
Roof and bathroom areas combine a horizontal face with an optional vertical upstand or wall band; basement waterproofing is calculated as a purely vertical external wall face. Switching on Multiple Sections lets you add several same-type areas (e.g. three bathrooms, or a stepped roof) in one run — each keeps its own dimensions and parapet/shower-wall choice, and the calculator adds every section's area together automatically.
Step 2 — Convert Area to Square Feet
Area (sq ft) = Area (m²) × 10.7639
Every area figure in this calculator — treatment area, material sizing area, and each mode's sub-areas — is shown in both units side by side, using the standard 1 m² = 10.7639 sq ft conversion factor.
Step 3 — Add Wastage
Material Sizing Area (m²) = Base Treatment Area × (1 + Wastage % ÷ 100)
Wastage is applied to size how much material to buy, not to the physical area — the actual treated area is always the Base Treatment Area from Step 1. This inflated figure only feeds into Step 4's material-quantity calculation, covering material used at detailing points (corners, joints, upstands) beyond the flat-area coverage rate, and off-cuts at sheet membrane joints.
Step 4 — Material Quantity (Coating vs Sheet)
Coating/Membrane: Material (kg) = Material Sizing Area × Coverage Rate per Coat × Number of Coats
Sheet: Effective Roll Coverage = (Roll Length × Roll Width) × (1 − Overlap % ÷ 100)
Sheet: Rolls Needed = ROUND UP(Material Sizing Area ÷ Effective Roll Coverage)
Cementitious and liquid/PU membrane systems are estimated by weight based on coverage rate and coat count; bituminous sheet membrane is estimated by roll count, with overlap reducing each roll's usable coverage.
Step 5 — Primer (Optional)
Primer Required (kg) = Material Sizing Area × Primer Coverage Rate
Primer Cost = Primer Required (kg) × Primer Rate per kg
Primer is modelled as a single, separate coat over the same material sizing area — at its own (typically lower) coverage rate — independent of the main coating or sheet method, since many liquid/PU membrane and sheet membrane systems specify a primer coat before the main material.
Step 6 — Calculate Cost (Optional)
Coating/Membrane: Material Cost = Material (kg) × Rate per kg
Sheet: Material Cost = Rolls Needed × Price per Roll
Labour Cost (rate per m²) = Material Sizing Area (m²) × Labour Rate per m²
Labour Cost (rate per sq ft) = Material Sizing Area (sq ft) × Labour Rate per sq ft
Total Cost = Material Cost + Primer Cost + Labour Cost
Labour can be priced per square metre or per square foot — the sq ft option matches the common Indian labour-rate convention — and either way the calculator converts it to an equivalent per-m² rate before computing labour cost.
Real-World Waterproofing Calculation Example
This example uses the active calculator mode, material type, and inputs above and follows the same steps from the formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Area type | bathroom | Determines the treatment-area geometry used |
| Material type | cementitious | Determines coating-weight vs sheet-roll calculation method |
| Wastage | 10% | Adds allowance before material quantity is calculated |
Step 1 — Treatment Area
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Floor area | Length × width | 5.00 m² (54 sq ft) |
| Wall band area | Perimeter × wall band height | 2.70 m² (29 sq ft) |
| Base treatment area | Sum of the above | 7.70 m² (83 sq ft) |
Step 2 — Convert Area to Square Feet
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Base treatment area in sq ft | 7.70 × 10.7639 | 83 sq ft |
Step 3 — Wastage
This step only sizes how much material to buy — the treated area stays the Base Treatment Area from Step 1.
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Extra material-sizing area from wastage | 7.70 × (10 ÷ 100) | 0.77 m² (8 sq ft) |
| Material sizing area (incl. wastage) | 7.70 + 0.77 | 8.47 m² (91 sq ft) |
Step 4 — Material Quantity
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Material per coat | 8.47 × 1.5 kg/m² | 12.7 kg |
| Total material (2 coats) | 12.7 × 2 | 25.4 kg |
Therefore, for this bathroom waterproofing job you have 7.70 m² (83 sq ft) of treated area — about 25.4 kg of material.
This page keeps things focused on the calculation above. For the full construction guide — verification checklist, reference tables, usage steps, tips, common mistakes, and limitations.See the complete Waterproofing Calculator.
Related Calculators
Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.