Screed calculator — how many bags of screed do you need?
The floor screed calculator works out the quantity of screed mix needed for a concrete or anhydrite floor. Enter the area in m², the screed thickness in centimetres and the material type (cement screed, anhydrite or fast-drying screed). The calculator uses the appropriate material density and returns the mass in kg, the volume in m³ and the minimum number of 25 kg bags.
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How we calculate the screed quantity
We calculate the volume of screed as the product of the area and the thickness (converted from cm to m). We then multiply by the density of the chosen material: cement screed 2,000 kg/m³, anhydrite 2,100 kg/m³, fast-drying screed 1,800 kg/m³. The number of bags is obtained by dividing the mass by 25 and rounding up.
Example calculation
Cement screed: 20 m², thickness 5 cm, density 2,000 kg/m³: volume = 20 × 0.05 = 1 m³, mass = 1 × 2,000 = 2,000 kg, bags = ceil(2,000 / 25) = 80 bags. Anhydrite (2,100 kg/m³): 20 × 0.05 × 2,100 = 2,100 kg = 84 bags.
Frequently asked questions
How do I calculate the amount of floor screed needed?
Screed quantity (kg) = area (m²) × thickness (m) × density (kg/m³). Density depends on type: cement screed ~2,000 kg/m³, anhydrite ~2,100 kg/m³, fast-drying ~1,800 kg/m³. Example: 20 m², 5 cm, cement: 20 × 0.05 × 2,000 = 2,000 kg = 80 × 25 kg bags.
What is the standard floor screed thickness?
Standard cement screed thickness for underfloor heating: 5–6 cm (at least 3 cm above the pipes). Without underfloor heating: minimum 3–4 cm for cement, 3 cm for anhydrite. For heavy loads (garage, warehouse): 8–15 cm. Too thin screed cracks; too thick unnecessarily loads the floor slab.
What is the difference between cement and anhydrite screed?
Cement screed: cheaper, moisture-resistant, suitable for bathrooms and outdoors, needs 4–6 weeks to cure. Anhydrite screed: self-levelling (flatter surface), ready to use after 7–14 days, lighter, cannot be used in wet areas without additional waterproofing. Choice depends on intended use and budget.
What is fast-drying screed and when should I use it?
Fast-drying (quick-setting) screed achieves usable strength after just 24–48 hours (instead of 4–6 weeks for standard cement). It is used in renovations requiring fast return to service, in commercial construction with tight schedules and in modernisation projects. It is more expensive than standard screeds.
How many bags of screed do I need and what bag sizes are available?
Screed is usually sold in 25 kg or 30 kg bags. The calculator gives the minimum number of 25 kg bags. For 20 m² at 5 cm depth you need 2,000 kg = 80 × 25 kg bags. Always order 5–10% extra for mixing losses and thickness corrections.
How should I prepare the substrate before pouring screed?
Proper substrate preparation is key to screed durability: 1) Clean of dust, grease and loose particles. 2) Prime absorbent substrates. 3) Lay insulation film or polystyrene (if thermal/acoustic insulation is required). 4) Fix expansion tape along all walls. 5) Set guide rails at the correct height. 6) Only then pour the screed.
When can I walk on the screed and lay the floor covering?
Cement screed: walk after 1–2 days, lay flooring after 4–6 weeks (moisture below 2%). Anhydrite: walk after 24–48 h, lay flooring after 7–14 days (moisture below 0.5%). Fast-drying: walk after 24 h, lay flooring after 2–7 days. Always check moisture with a meter before laying parquet or laminate.
How much does floor screed cost in Poland (materials and labour)?
Material costs per 25 kg bag: cement screed 20–35 PLN, anhydrite 30–50 PLN, fast-drying 50–80 PLN. For 20 m² at 5 cm (80 bags): cement ~1,600–2,800 PLN, anhydrite ~2,400–4,000 PLN. Labour: 20–45 PLN/m², so 20 m² = 400–900 PLN. Total cost for 20 m²: 2,000–3,700 PLN.
Can I do floor screed myself?
Cement screed can be done yourself, but requires effort and proper equipment (a mixer or electric paddle, guide rails, a level and a float). Anhydrite screed is more difficult — it requires special mixing and spreading. For areas over 30–40 m², consider hiring a pump or a crew, especially for anhydrite.
What are the most common mistakes when pouring screed and how can I avoid them?
1) Too thin — screed cracks under load; always use at least 3–4 cm. 2) No expansion joints at walls — screed cracks from thermal stress; always fit expansion tape. 3) Drying too quickly — cover with film for 3–7 days. 4) Pouring on a wet substrate — dry to below 5% moisture. 5) Wrong mix ratios — follow the manufacturer's instructions strictly.
Results are indicative. We recommend ordering 5–10% more material to allow for mixing losses and possible thickness adjustments. This result is not a structural design.