How to use the plastering / render calculator
This calculator helps you convert an area and coat thickness into a mix volume and bag quantity. It is intended for quantity takeoffs, early budgets and checks against a measured schedule. Start with the dimensions or quantities for one clearly defined item of work. Enter values in the units shown beside each field; millimetres and metres are not interchangeable.
Uses a uniform finished thickness and a user-entered mixed yield per bag. The default yield is illustrative; proprietary mixes vary. Substrate levelling, multiple coats and wastage require separate allowances.
Worked example
At 30 m², each 10 mm of thickness requires 0.3 m³. A 50 mm screed therefore needs 1.5 m³ before wastage.
Before you order
Compare the result with your drawings and supplier information. Keep the original net quantity separate from allowances, and round purchasing quantities only at the ordering stage. Check whether delivery, labour and related materials belong elsewhere in your estimate. If the drawing or specification changes, update the inputs and record the revised basis instead of reusing an earlier total.
For the concepts behind this calculation, read Screed, Wastage Factor, Unit Rate.