Plaster Calculator
Estimate cement, sand, water and total plaster volume for any wall or ceiling — with engineering drawings and a printable PDF report.
Material cost estimate (optional)
How to estimate plaster
Three simple steps to a complete cement, sand and water estimate.
Wall, ceiling, internal or external — choose the surface so the right thickness and mix are suggested.
Add length, height, plaster thickness, mix ratio and wastage. Metric and imperial both work.
Total area, wet and dry volumes, cement bags, sand volume, water needs and optional cost — clearly broken down.
Plaster Calculator — Free & Accurate
Our plaster calculator helps builders, plasterers, contractors, and DIYers estimate the cement and sand needed for any wall or ceiling. Pick a plaster type — wall, ceiling, internal, or external — enter the surface dimensions, plaster thickness, and mix ratio, and get a complete material list in seconds.
The calculator applies the standard 1.33× dry-volume correction (cement mortar shrinks ~33% when wet, so you need 33% more dry material than the final wet volume) and lets you add a wastage buffer from 0% to 20% for site losses. Pick from standard mix ratios (1:3 rich, 1:4 standard internal, 1:5 standard external, 1:6 ceiling) or define a custom cement-to-sand ratio. Bulk density 1,440 kg/m³ for cement; water is estimated at 0.5 × cement weight, matching typical plaster w/c ratios.
Results show total area, wet and dry mortar volumes, cement quantity (kg and 50 kg bags), sand volume, water needs, and an optional cost estimate including cement, sand, and labor in your local currency. Everything runs in your browser — no signup, no data sent to any server.
Why use this calculator?
Built for the site, not the spec sheet — simple, fast, and accurate.
No spreadsheets, no formulas to memorise. Type your sizes, hit calculate, and you're done.
Applies the 1.33× dry-volume correction, mix-ratio math, and wastage like a site engineer would.
Everything runs in your browser. Your dimensions never leave your device.
Mix metres, feet, inches, and centimetres on the same job — the math converts cleanly.
Tells you total area, cement bags, sand volume and water — exactly what your supplier and labour need.
Open it on your phone right at the workshop. Fully responsive, no app needed.
Related construction tools
Free, browser-based, and built the same way as the plaster calculator.
Frequently asked questions
For internal walls, 1:4 (cement to sand) is the typical default. For external walls exposed to weather, use 1:5 — a leaner mix is more flexible and less likely to crack. Ceilings often use 1:6 because they don't need to bear loads. For thin finishing coats, 1:3 is rich enough to bond well. If your supplier or specification calls for a different ratio, pick "Custom mix" and enter the exact cement-to-sand parts.
We start with the wet plaster volume (area × thickness), then apply the 1.33× dry-volume factor — cement mortar shrinks ~33% when wet, so you need 33% more dry material than the final installed volume. The dry volume is split by the mix ratio into cement and sand, then both are scaled up by your wastage percentage. Cement is reported in kg and 50 kg bags using a bulk density of 1,440 kg/m³.
The estimate uses a 0.5 water-to-cement ratio by weight, which gives a workable plaster mortar slump. So if you need 50 kg of cement, plan for around 25 litres of water. Adjust on site based on the mix's feel — drier days and dry substrates absorb more water; wet sand reduces what you need to add. Always add water gradually.
12 mm (about ½ in) is standard for internal walls. External walls usually need 15–20 mm in one or two coats for weather protection. Ceilings are usually 8–10 mm thin. Single-coat internal plaster is typically 12 mm; if you're doing a double coat (scratch + finish), allow 20 mm total. For very smooth finishes over a base plaster, a 6 mm setting coat is common.
Yes. Every dimension has its own unit picker, so you can enter the wall length in feet, the height in metres, and the plaster thickness in inches or millimetres on the same calculation. The math converts everything to consistent units internally.