Rendering Quantity Calculator
About This Calculator
This rendering calculator helps you determine the quantity of render needed for external walls. Whether you're rendering a new extension, re-rendering an existing property, or applying a decorative finish, getting the right quantity is essential for budgeting and ordering.
The calculator accounts for different render types, number of coats, and includes a wastage allowance for accurate ordering.
Render Types
Sand & Cement Render
The traditional choice — hard-wearing and economical. Coverage: ~1.2m² per 25kg bag at 10mm. Mix ratio typically 1:4 (cement:sand).
Lime Render (Traditional)
Breathable and flexible, ideal for older properties. Better coverage than cement: ~1.5m² per 25kg bag at 10mm. Traditional mix: 1:1:6 (cement:lime:sand).
Polymer Modified Render
Pre-mixed render with added polymers for improved adhesion and flexibility. Coverage: ~1.3m² per 25kg bag at 10mm.
Insulating Render System
Contains insulating aggregates to improve thermal performance. Thicker application required. Coverage: ~0.8m² per 25kg bag at 10mm.
Typical Render Systems
| System | Coats | Total Thickness |
|---|---|---|
| Traditional | 2 coats | 15-20mm |
| Scratch + Brown + Finish | 3 coats | 20-25mm |
| Single Coat | 1 coat | 10-15mm |
| Insulating Render | 1-2 coats | 20-30mm |
Example Calculations
Gable End Wall
A wall 8m × 5m with traditional 2-coat sand & cement render (10mm per coat):
- Wall area: 40 m²
- Total thickness: 20mm
- Bags required (10% wastage): ~37 bags
- Mix ratio: 1:4 cement to sand
Period Property (Lime)
A cottage wall 6m × 4m with lime render (12mm per coat, 2 coats):
- Wall area: 24 m²
- Total thickness: 24mm
- Bags required: ~18 bags
- Mix ratio: 1:1:6 (cement:lime:sand)
Extension (Polymer)
An extension 10m × 2.4m with single-coat polymer render (15mm):
- Wall area: 24 m²
- Total thickness: 15mm
- Bags required: ~28 bags
Application Tips
- Always apply render onto a suitable base — use render beads at edges
- Dampen the substrate before application (but not soaking wet)
- Apply scratch coat and allow to cure before second coat
- Protect fresh render from sun, wind, and rain during curing
- Add 10-15% wastage allowance for cuts, waste, and touch-ups
- Consider using a plasticiser in the mix for workability
Ready to Calculate?
Enter your wall dimensions and get instant render quantity calculations.
Open Calculator →Related Calculators
References & Sources
Standards Cited
- ASTM C926 — Standard Specification for Application of Portland Cement-Based Plaster
Defines external render/stucco systems, coat thicknesses, and application methods - ASTM C1063 — Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster
Specification for substrate preparation and lath installation for stucco/render
Formulas Used
- Render volume:
volumeM3 = wallArea x (thickness x numberOfCoats / 1000)
Source: ASTM C926 - Render weight:
weightKg = volumeM3 x density x (1 + wastage/100)
Source: ASTM C926 — Densities: sand-cement/lime/polymer ~2000 kg/m3, insulating ~800 kg/m3 - Bags required:
bagsRequired = ceil((wallArea x totalThicknessMm/10 / coveragePerBag) x (1 + wastage/100))
Source: ASTM C926 — Coverage per 25kg bag at 10mm: sand-cement 1.2 m2, lime 1.5 m2, polymer 1.3 m2, insulating 0.8 m2
Key Assumptions
- Render densities: sand-cement/lime/polymer approximately 2000 kg/m3, insulating approximately 800 kg/m3 — ASTM C926
- Recommended mix ratios: sand-cement 1:4 + plasticiser, lime 1:1:6, polymer and insulating are pre-mixed — ASTM C926 / ASTM C1063
- Coverage per 25kg bag at 10mm thickness: sand-cement 1.2 m2, lime 1.5 m2, polymer 1.3 m2, insulating 0.8 m2 — ASTM C926
- Typical wastage allowance of 10-15% for render — Industry standard practice