Rendering Calculator UK
Calculate how many bags of render you need for your project. Add multiple walls, deduct windows and doors, and choose your render type to get a bag count and weight estimate.
Enter wall details
Typical: 15-20mm for 2-coat external, 10-15mm for monocouche
Covers cuts, breakages and uneven ground. 10% is a typical starting point.
Render estimate
Enter at least one wall with length and height to see your estimate
How to calculate how much render you need
The calculation works in three steps: measure the gross wall area (length x height for each wall), deduct the area of windows and doors, then multiply the net area by the render thickness and density.
Coverage rates for render are typically quoted as kg per m2 per mm of thickness. Dividing total kg by bag size gives bag count. Always add wastage - render waste is significant on most projects due to mixing, over-ordering to avoid running short, and the messy nature of the work.
Render type coverage guide
| Render type | Thickness | Approx bags/m2 | Note |
|---|---|---|---|
| Sand:cement 2-coat (external) | 15-20mm | ~1.2-1.5 bags/m2 | Most common external system |
| Sand:cement 1-coat (internal) | 10-12mm | ~0.7-1.0 bags/m2 | Internal walls only |
| Monocouche | 12-15mm | ~1.0-1.2 bags/m2 | Through-colour, no painting needed |
| Pre-mixed bag render | Variable | Check product label | Varies significantly by brand |
Coverage rates are estimates. Always verify against your specific product data sheet before ordering.
Common rendering mistakes
- Applying too thick in one coat. Thick single coats sag and crack. Apply in two coats with adequate drying time between them.
- Not soaking the substrate. Dry brick or block will suck moisture from the render too fast, preventing proper hydration. Dampen the wall before applying.
- Rendering in direct sunlight or frost. Rapid drying and freezing both damage fresh render. Cover with breathable hessian or polythene to protect in extreme conditions.
- Skimping on wastage. Running out of render mid-wall is a common and frustrating problem. Order at least 15% extra - it is always better to have a bag left over than to need one more.
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Frequently asked questions
Planning estimates only
These results are estimates for planning purposes only. Actual material quantities can vary based on site conditions, compaction, wastage, product size, installation method and supplier guidance. For structural, safety-critical or regulated work, always consult a qualified professional.