Plaster Calculator

Calculate how much plaster or render a wall needs, based on the net wall area, the layer thickness and the consumption printed on the bag.

Formula and method

Net wall area (gross area minus openings) is multiplied by the layer thickness to give a volume, and by the consumption rate to give the required mass. That mass is divided by the bag weight and rounded up.

How to measure the inputs

Measure each wall's length and height and multiply by the number of identical walls.
Add up the area of doors and windows you want to deduct.
Read the consumption rate and bag weight from the bag you will actually use.

Worked example

Wall length 16.4 ft; Wall height 9.84 ft; Wall count 1; Openings area (optional) 5.38 ft²; Layer thickness 0.39 in; Consumption rate 3; Package weight 8.82 lb; Waste 10 % → Plaster bags: 120

Practical tips

Order whole bags — an opened bag absorbs moisture and goes off quickly.
Apply in two passes on thick layers rather than one heavy coat.
Check the substrate is not too dry or too absorbent before starting.

Assumptions

The layer thickness is uniform across the wall, which is rarely exactly true in practice.
Consumption per m² per mm comes from the product datasheet.
Beads, corner profiles and bonding agents are not included.

Frequently asked questions

What does the consumption rate mean?

It is the dry material needed per square metre per millimetre of thickness. A product with 9 kg/m²/mm at 10 mm thickness uses 90 kg per m².

Which thickness should I enter?

Enter the average thickness. Walls are never perfectly flat, so measuring the deepest point gives a safer estimate for patch repairs.

Do doors and windows reduce the plaster I need?

For large openings, yes — but remember that reveals and corners still need plaster and corner beads.

Does this cover skimming and rendering?

Both, if you know the consumption rate. Renovation skimming is usually 2–3 mm thick and backing coats 10–20 mm.

Related calculators

Estimate only

Results are material quantity estimates only. They are not structural design, and they are not a substitute for local building codes, engineer approval or manufacturer instructions.

Browse by category

Walls