Render calculator: sand and cement per coat
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| Render system | Sand and cement |
| Wall area | Wall: rectangle 5 m × 4 m |
| Coats | Scratch coat: thickness 12 mm, mix: parts sand to 1 part cement 3 parts; Top coat: thickness 8 mm, mix: parts sand to 1 part cement 4 parts |
| Waste allowance | 10% |
| Dry-volume factor | 1.3 × |
| Cement density | 1,440 kg/m³ |
| Sand density | 1.5 t/m³ |
| Cement bag size | 25 kg |
| Sand bulk bag size | 0.85 t |
| Reinforcing mesh over the whole wall | No |
Order: 8 × cement bags and 0.66 t of sand
| Result | Value |
|---|---|
| Cement bags | 8 |
| Cement | 189.4 kg |
| Sand | 660.7 kg |
| Sand bulk bags | 1 |
| Wall area (after openings) | 20 m² |
| Coat | Thickness | Mix (cement:sand) | Cement | Sand |
|---|---|---|---|---|
| Scratch coat | 12 mm | 1:3 | 123.6 kg | 386.1 kg |
| Top coat | 8 mm | 1:4 | 65.9 kg | 274.6 kg |
Show the working
- Wall area: 20 m² − 0 m² of openings = 20 m²
- Scratch coat: 20 m² × 12 mm × 1.1 (10% waste) = 0.264 m³ wet; × 1.3 = 0.343 m³ dry
- Scratch coat at 1:3: cement 0.343 ÷ 4 × 1,440 kg/m³ = 123.6 kg; sand 0.343 × 3 ÷ 4 × 1.5 t/m³ = 0.386 t
- Top coat: 20 m² × 8 mm × 1.1 (10% waste) = 0.176 m³ wet; × 1.3 = 0.229 m³ dry
- Top coat at 1:4: cement 0.229 ÷ 5 × 1,440 kg/m³ = 65.9 kg; sand 0.229 × 4 ÷ 5 × 1.5 t/m³ = 0.275 t
- Total: cement 189.4 kg, sand 0.661 t
- Cement bags: 189.4 kg ÷ 25 kg, rounded up = 8
- Sand bulk bags: 0.661 t ÷ 0.85 t, rounded up = 1
How it works
- Per coat: wet volume (m³) = area × coat thickness × (1 + waste); dry volume = wet × dry-volume factor
- Per coat at 1 : r (cement : sand): cement (kg) = dry ÷ (1 + r) × cement density; sand (t) = dry × r ÷ (1 + r) × sand density
- Totals add the coats; cement bags = cement ÷ bag size, sand bulk bags = sand ÷ bulk bag size, both rounded up
- Monocouche or basecoat (kg) = area × thickness (mm) × coverage (kg/m²/mm) × (1 + waste); thin-coat finish (kg) = area × kg/m² × (1 + waste)
- Beads (m) = the perimeter of each opening plus any corner, stop and bellcast bead you add
Coat thicknesses and mixes vary with the background and exposure: follow the render maker's specification or BS EN 13914-1.
Mesh is shown as wall area only: add the overlap the mesh maker asks for.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Waste allowance | 10 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 PL2 (test RN1 uses 10%). Researcher to confirm against render makers' guidance. |
| Dry-volume factor | 1.3 × | Our assumption Not yet checked against the source | Our choice: change it to suit your job Dry materials shrink when mixed with water. Researcher to check against cement makers' guidance. |
| Cement density | 1440 kg/m3 | Our assumption Not yet checked against the source | Our choice: change it to suit your job Typical planning figure with no source yet. Researcher to source it and reclassify as typical. |
| Sand density | 1.5 t/m3 Sources range 1.4–1.6 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) |
| Cement bag size | 25 kg | Common UK size Not yet checked against the source | From your product Common UK cement bag. |
| Sand bulk bag size | 0.85 t | Common UK size Not yet checked against the source | builder.tools bulk bag figure (checked 19 October 2026) Varies by merchant; check yours. |
Regulations and standards
- BS EN 13914-1 (external render): coat thicknesses and mixes, Researcher to confirm against the standard and render makers
Our checks use the guidance for England unless a badge says otherwise. Wales, Scotland and Northern Ireland have their own rules: check the source for where you live.