Floor screed is sold by weight, so the bags you need depend on the volume and how heavy the dry mix is per millimeter. 20 m² of sand-cement screed, 50 mm thick, at 2 kg per m² per mm, with 5% extra: 20 × 50 × 2 × 1.05 = 2,100 kg, or 84 bags of 25 kg. Choose the type, type the area, the thickness and the consumption printed on the bag, and the calculator gives bags, weight, volume, what one bag covers and the cost.
Bags for 10 m², with 5% extra
| Type | Thickness | Per m² | Total | 25 kg bags |
|---|---|---|---|---|
| Self-leveler (1.65 kg/m²/mm) | 3 mm (1/8 in) | 4.9 kg | 52 kg | 3 |
| Self-leveler | 5 mm (3/16 in) | 8.3 kg | 87 kg | 4 |
| Self-leveler | 10 mm (3/8 in) | 16.5 kg | 173 kg | 7 |
| Sand-cement screed (2 kg/m²/mm) | 25 mm (1 in) | 50 kg | 525 kg | 21 |
| Sand-cement screed | 50 mm (2 in) | 100 kg | 1,050 kg | 42 |
| Sand-cement screed | 65 mm (2½ in) | 130 kg | 1,365 kg | 55 |
| Sand-cement screed | 75 mm (3 in) | 150 kg | 1,575 kg | 63 |
The step from a thin leveler to a real screed is huge: 10 m² at 50 mm weighs over a tonne, which matters for carrying the bags upstairs and for mixing by hand.
Measure the real thickness
A floor is rarely flat. Stretch a string or lay a long straightedge across it and measure the gaps: the average depth, not the thinnest spot, sets the quantity. A few millimeters more over a whole room add bags quickly, which is why the calculator adds 5% by default.
Self-leveler or screed?
Self-leveling compound is for smoothing an existing floor before tiles, vinyl or wood, usually a few millimeters at a time. A sand-cement screed builds up height, covers underfloor heating pipes and evens out a structural slab. Mixing instructions, primers and the time before you can lay flooring are on each product’s datasheet.
The calculator works offline once saved, so it is ready on site.
Frequently asked questions
How much screed do I need per square meter?
Thickness in mm × the consumption on the bag. Sand-cement screed at about 2 kg per m² per mm, 50 mm thick, takes 100 kg per m²; a self-leveler at 1.65, 5 mm thick, about 8.3 kg per m².
How many bags of self-leveling compound for 10 m²?
At 5 mm and 1.65 kg per m² per mm, with 5% extra: 10 × 5 × 1.65 × 1.05 = 87 kg, or 4 bags of 25 kg.
How do I read the coverage on the bag?
If the bag says '1.6 kg/m² per mm', type 1.6. If it gives a coverage, such as '25 kg covers 3.8 m² at 4 mm', divide: 25 ÷ 3.8 ÷ 4 = 1.64.
How thick should a screed be?
A bonded sand-cement screed can be fairly thin, from about 25 mm; unbonded or floating screeds, such as over insulation, are usually 50–75 mm or more. Self-levelers are poured a few millimeters thick, within the range on the bag.
How long does screed take to dry?
The datasheet gives it. Self-levelers can often be walked on within hours, while thick sand-cement screeds take weeks before moisture-sensitive flooring can go down.
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