Screed calculator — how many bags of screed do you need?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.