Plaster

The plaster calculator estimates how much plaster and water you need to finish a wall. Enter the wall dimensions and the plaster thickness to get the bag count for a smooth interior finish.

Common use cases

How to use this calculator

  1. Enter the wall length and height.
  2. Enter the plaster thickness in millimetres.
  3. Press Calculate to see the plaster weight needed.
  4. Use the bag estimate to plan your order.

Example calculation

A 5 m × 2.5 m wall (12.5 m²) with a 10 mm finish needs about 163 kg of plaster (around 7 bags of 25 kg) and 49 L of water.

Frequently asked questions

How much plaster do I need per square metre?

Roughly 1.3 kg per m² per millimetre of thickness — a 10 mm finish needs about 13 kg per m².

How thick should a plaster coat be?

Skim coats are 2–3 mm; bonding and undercoat layers are typically 8–11 mm thick.

How much water do I add to plaster?

About 0.3 L per kg of plaster — always follow the bag instructions for exact ratios.

Can I plaster over old plaster?

Yes if the substrate is sound; otherwise apply a bonding agent or remove loose material first.