Plaster and Render Calculator
Estimate wet plaster or render volume and bags from area, thickness and product yield.
Last reviewed September 19, 2026
Result
Enter surface areas and wet-volume yield per bag to see the result.
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Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use it
- Add each rectangular wall, ceiling or surface section.
- Enter the combined area of openings to subtract.
- Enter the total finished thickness for the product being calculated.
- Enter wet-volume yield per bag from the exact label, then add any allowance.
How it is calculated
Measured surfaces are summed before openings, thickness and product yield are applied:
Net area = gross surface area − openings
Wet volume = net area × total thickness
Bags = ceil(wet volume with allowance ÷ wet yield per bag)The label yield is required because plaster and render formulations differ.
Product and substrate checks
Use the exact product sheet. Yield can depend on water addition and application thickness. Do not substitute a generic bag weight conversion.
Calculate different coats separately. Basecoat, finish plaster, render and reinforcement layers may use different materials and thicknesses.
Check the background. Suction, contamination, movement and flatness affect preparation and material consumption. Follow the system manufacturer’s method.
Respect working time. Mix only quantities that can be applied within the stated pot life and conditions. This calculator is an order estimate, not a mixing instruction.
With your numbers
- Net area = 200 ft² − 0 ft² = 200 ft²
- Wet volume = net area × 0.375 in thickness
- With 0% extra = 6.25 ft³
- Divide by the entered wet yield and round up to 14 bags
Quick reference
No extra is added by default. Use Custom for surface variation, mixing loss and the product guidance for the substrate.
| Job | Product bags to buy |
|---|---|
| 200 ft² at 3/8 in | 14 |
| 400 ft² at 1/2 in | 38 |
| Two walls minus openings | 20 |
| 100 ft² patch area | 5 |
| 100 m² at 10 mm | 80 |
| 50 m² at 15 mm | 60 |
Common questions
- How many bags for 100 square metres at 10 millimetres?
- The exact wet volume is 1,000 L. With 10% extra and a labelled yield of 12.5 L per bag, the result is 88 bags.
- Why enter wet-volume yield instead of bag weight?
- Products with the same bag weight can have different mixed yields. Wet yield connects the measured layer volume directly to the manufacturer’s product.
- Can base and finish coats be combined?
- Only when they use the same product and yield. Different base, finish or reinforcement coats should be calculated separately.
- Does thickness include surface variation?
- Enter the intended average finished thickness. Use the custom allowance for reasonable variation, and investigate unusually uneven backgrounds before ordering.