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Plaster and Render Calculator

Enter the area and thickness to get the volume of plaster or render. Add the consumption printed on the bag (kg per m² per mm) and the bag weight to get the kilograms and number of bags to buy, with a waste allowance. 30 m² at 10 mm thick is 0.3 m³ before waste.

Measurements

Units

kg per m² per mm of thickness, as printed on the product.

Optional: to count bags.

Results

Volume

0.38 yd³

Enter the consumption from the product to get kilograms and bags.

Show the working
  1. Volume300 ft² × 0.37 in × (1 + 10%) = 0.38 yd³
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How to use the plaster calculator

  1. Choose Metric or Imperial.
  2. Enter the area to plaster or render.
  3. Enter the thickness.
  4. Enter the product’s consumption (kg per m² per mm) and the bag weight.
  5. Set a waste allowance.

How the calculation works

Volume = area × thickness × (1 + waste). Dry product = area × thickness in mm × consumption × (1 + waste). Bags = ⌈dry product ÷ bag weight⌉.

Worked examples

Living room walls. 30 m² at 10 mm: 0.3 m³, or 0.33 m³ with 10% waste. If the bag says the consumption is a given number of kilograms per m² per mm, the calculator multiplies 30 × 10 × that figure × 1.1 and divides by the bag weight.

US ceiling. 300 ft² at ⅜ in: about 0.35 yd³ before waste.

How to interpret the results

Round up to whole bags and check the product’s shelf life; buy enough to finish each wall in one go to avoid visible joins.

Tips and common mistakes

  • Prepare the background as the product requires: bonding agents, mesh or dampening.
  • Measure the thickest areas; filling hollows can double local thickness.
  • Don’t mix more than you can use within the working time.
  • Keep bags dry; damp plaster sets badly.

Plaster, render and coats

Interior plaster and exterior render are applied in one or more coats, and products for each coat often have different consumption figures and recommended thicknesses. Run the calculator once per coat and product, then add the results. Bags carry the consumption per millimetre so you can scale it to your thickness. If you are filling deep hollows, measure them separately and add their volume, because the average thickness across the wall can hide a lot of extra material in a few low spots.

Use the square footage calculator for the wall and ceiling areas, the drywall calculator if you are boarding instead of plastering, and the wallpaper calculator for the finish. Add the bags to the project materials list to keep track of everything for the room.

Assumptions and limitations

The calculator assumes an even thickness over the area. It doesn’t account for beads, mesh or corner details.

Frequently asked questions

How do I calculate how much plaster I need?

Multiply area × thickness (mm) × the product’s consumption in kg per m² per mm. Divide by the bag weight and round up to get the number of bags.

Where do I find the consumption figure?

On the bag or the product data sheet, usually as kg per m² per mm of thickness. It varies between products, so the calculator doesn’t assume one.

How thick should plaster or render be?

It depends on the product and the background. Follow the manufacturer’s recommended thickness for each coat.

How much extra should I allow?

Uneven walls take more material. The calculator starts at 10%.

Does it work for several coats?

Run it once per coat with that coat’s thickness, or add the thicknesses if the same product is used.

What is the difference between plaster and render?

Plaster usually refers to interior wall and ceiling finishes, while render is applied to exterior walls and is formulated to resist weather. Both are estimated the same way here, using the consumption figure for the specific product.

Why is my plaster estimate higher than the bag coverage?

Bag coverage is usually quoted for a specific thickness on a flat surface. Thicker coats, uneven backgrounds and waste all increase the quantity.

Sources