Wall Plaster Quantity Calculator

Work out wall plaster quantity instantly with clear inputs, formula shown and shareable results.

About Wall Plaster Quantity Calculator

Bag coverage is quoted at a reference thickness, so it scales inversely with the thickness actually applied: a bag covering 9 square metres at 10 mm covers only 6.9 at 13 mm. Add 10% for wastage since plaster that goes off in the bucket cannot be reused.

Formula

Plaster quantity

coverage at thickness t = quoted coverage x 10 / t; bags = ceil(area x (1 + wastage) / coverage)

Worked example

With the default values below, Wall Plaster Quantity Calculator returns Bags required of 6. Change any input above and every figure here is recalculated in your browser.

Inputs used

Area to plaster: 32 m²
Plaster thickness: 13 mm
Bag coverage at 10 mm: 9 m²/bag
Wastage: 10 %

Results

Bags required: 6 bags
Plaster volume: 0.42 m³
Effective coverage at this thickness: 6.92 m²/bag
Total plaster weight: 150.00 kg

Step by step

1Values used
2Plaster quantity
3Bags required= 6 bags
4Plaster volume= 0.42 m³
5Effective coverage at this thickness= 6.92 m²/bag
6Total plaster weight= 150.00 kg

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why can plaster not be reused?

Gypsum plaster sets chemically. Once it has started to go off, re-tempering with water destroys the strength and finish.

What thickness is normal?

2-3 mm for a skim over plasterboard, 11-13 mm for a float and set on masonry in two coats.