Screed and Self-Levelling Compound Calculator (Bags for a Floor)
Kilos and bags of self-levelling compound or screed for a floor, using the average thickness of a layer that is thin at one end and thick at the other.
Results
The dashed line marks the value you entered.
What this tool does
A layer of 1 mm over 1 m² is exactly 1 litre, so the volume is just area × average thickness in mm; the product's consumption in kg per m² per mm turns that into weight. Self-levelling compounds commonly use about 1.6–1.8 kg/m² per mm and a cement–sand screed about 2 — the figure is on the bag, so check the datasheet, along with the minimum and maximum thickness it allows. Floors are rarely flat or truly level: take the thinnest and thickest points from a level or laser and the average of an evenly sloping layer is halfway between them. Add a margin for waste and for the primer coat's absorption.
Formula
average thickness = (thinnest + thickest) ÷ 2 · product = area × average thickness (mm) × consumption (kg/m²/mm) × (1 + waste)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
ar | Area of the floor | m² |
tm | Thinnest point of the layer | mm |
tx | Thickest point of the layer | mm |
cn | Consumption of the product (kg per m² per mm) | kg/m²/mm |
bg | Size of a bag | kg |
ws | Extra for waste and uneven ground | % |
KG | Product to order, with the margin | kg |
BG | Bags | — |
MN | Average thickness | mm |
VL | Volume of the layer | L |
Worked example
- Area of the floor20 m²
- Thinnest point of the layer5 mm
- Thickest point of the layer15 mm
- Consumption of the product (kg per m² per mm)1.7 kg/m²/mm
- Size of a bag25 kg
- Extra for waste and uneven ground5 %
- Product to order, with the margin357 kg
- Bags15
- Average thickness10.0 mm
- Volume of the layer200 L
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- Always order a little more material than the calculated quantity. Cuts, breakage and pattern matching create waste that depends on the shape of the job.