Enter your sizes
Assumptions (change if your office uses different constants)
Result
For a ceiling, enter its length and width as length and height, with one face.
How it’s calculated
Questions
How much cement is needed for 100 sq ft of 12 mm plaster?
In 1:4 mortar, 100 sq ft (9.29 m²) of 12 mm plaster needs about 1 bag of cement with the usual allowances. In 1:6 it is about 0.7 bags. Enter your area for the exact figure.
Which mix and thickness should I use?
Commonly 12 mm in 1:4 or 1:6 for internal walls, 15–20 mm in 1:4 (often in two coats) for external walls, and 6 mm in 1:3 or 1:4 for ceilings — but follow the specification of your project or rate book item.
Why add 20% and multiply by 1.27?
The 20% covers filling joints and an uneven wall surface; 1.27 converts wet mortar to the dry volume of cement and sand. Both are rules of thumb — change them under Assumptions to match your office.
Need the full estimate, not just one item?
BESTimate makes the whole government-format estimate — Measurement, Abstract and Summary in Excel — with BMC, PWD, CPWD, MJP and CIDCO rates built in. Launching 26 November 2026 · first 99 to pre-register get 50% off for 6 months.