Screed Calculator
Enter area, thickness and bulk density – get all key figures for your project instantly
- Updated
Heating screed 5–6 cm, residential cement screed 4–6 cm, basement floors 6–8 cm.
Material and bag size2,000 kg/m³ · 40 kg bags
Cement screed approx. 2,000 kg/m³, anhydrite screed approx. 2,100 kg/m³.
Weight per bag
Bags needed
50bags
50For 20 m² at 5 cm thickness you need 1 m³ of screed (2,000 kg) – that is 50 bags of 40 kg.
- Volume
- 1 m³
- Weight
- 2,000 kg
How this was calculated
What you can do
Larger quantities: compare ready-mix
For larger projects, delivery as ready-mix (mixer truck) is cheaper than bagged material. From about 3 m³, compare prices with local concrete suppliers.
RZ-26 · headon.pro
Calculating screed: volume, weight and material needs
Cement, anhydrite and liquid screed – the key figures for building projects
The screed calculation starts with the volume: m³ = area (m²) × thickness (m). For 20 m² at 5 cm thickness, that comes to 1.0 m³. With the bulk density of cement screed (approx. 2000 kg/m³), the total weight follows: 1.0 m³ × 2000 kg/m³ = 2000 kg. Split across 40 kg bags, that is 50 bags. This simple chain is the basis of every screed calculation – whether for bagged material or ready-mix delivery.
Screed types and their properties: Cement screed (CT) is the most common type in Germany – affordable, robust and suitable for almost all applications. Anhydrite screed (CA), based on gypsum, dries faster but is more moisture-sensitive and not suitable for wet rooms. Liquid screed is poured as a self-levelling flow screed – it has lower internal stress and is therefore ideal for large underfloor-heating areas. Magnesite screed is rarely installed anymore, but is still found in the renovation of older buildings.
Standard thicknesses per DIN 18560: The German standard distinguishes between load classes. In residential areas on an insulation layer, cement screed requires a minimum thickness of 45 mm. With underfloor heating, the covering increases to at least 45 mm above the top of the pipe, which results in a total thickness of approx. 60–65 mm for 15 mm pipes. The thickness also determines the curing time: cement screed needs roughly one day per mm of thickness.
Structural load during installation: Screed is heavy – 2000 kg per m³. On a residential floor with 80 m² of area and 6 cm of screed, that adds up to almost 9.6 tonnes of extra load. When renovating old timber-beam ceilings or historic building structures, a structural engineer must check the load-bearing capacity before screed is poured. Lightweight screed (e.g. with expanded clay added) can reduce the bulk density to 1200–1600 kg/m³ – at the cost of compressive strength.
Screed types and typical applications
Overview of common screed mortars
- Cement screed (CT)
- Universally usable; 2000 kg/m³; suitable for wet rooms; 1 day/mm drying time
- Anhydrite screed (CA)
- Faster drying; 2100 kg/m³; NOT suitable for wet rooms; self-levelling option available
- Liquid screed
- Pumpable, self-levelling; ideal for underfloor heating; lower internal stress
- Heating screed
- Designed for hot-water underfloor heating; covering ≥ 45 mm above pipe per DIN
- Rapid-drying screed
- Ready to cover after 24–48 h; more expensive than standard; for time-critical projects
- Lightweight screed
- Expanded clay added; 1200–1600 kg/m³; for structurally weaker constructions
Calculation examples
- Volume (20 × 0.05)
- 1.00 m³
- Weight (1.00 × 2000)
- 2,000 kg
- Bags at 40 kg (⌈2000/40⌉)
- 50 bags
- Volume (30 × 0.08)
- 2.40 m³
- Weight (2.40 × 2000)
- 4,800 kg
- Bags at 40 kg (⌈4800/40⌉)
- 120 bags
Frequently asked questions about the screed calculator
Thicknesses, weight, drying time and screed types
What screed thickness is required for residential rooms?
The minimum thickness for cement screed on a separating layer (floating screed) is 45 mm (approx. 4.5 cm) in residential areas per DIN 18560. Special requirements apply with underfloor heating (heating screed): the screed covering above the pipes must be at least 45 mm, which can lead to a total thickness of 65–70 mm. In basement areas on insulation: 60–80 mm. The exact thickness is determined by the planner or screed installer.
How much does 1 m³ of screed weigh?
Cement screed (CT) has a bulk density of approx. 1900–2100 kg/m³, typically 2000 kg/m³. Anhydrite screed (CA) is slightly heavier: approx. 2000–2200 kg/m³, typically 2100 kg/m³. Magnesite screed is around 1700–1900 kg/m³. On a timber-beam ceiling with 100 m² and 6 cm of cement screed, that amounts to approx. 12 tonnes of extra load – an important factor for the structural calculation.
Bagged material or ready-mix – which is cheaper?
From about 2–3 m³ of screed, it is worth comparing prices with ready-mix (delivered by mixer truck). Bagged material costs approx. €5–10 per 40 kg bag – at around 50 bags per m³, that is €250–500/m³ – while ready-mix costs approx. €80–140/m³ depending on the region. Delivery costs and minimum order quantities for ready-mix (often 3 m³) also apply. For small areas and renovations, bagged material is more practical; for new-build floors from 50 m², ready-mix almost always pays off.
How long does screed need to dry?
Under normal conditions, cement screed needs approx. 1 day of drying time per mm of thickness – so approx. 45 days for 45 mm. Anhydrite screed dries faster: approx. 1 day per 2 mm, so approx. 22 days. Moisture testing (using the CM method) checks the actual residual moisture to confirm the screed is ready to cover. Flooring laid too early can swell, develop mould or come loose. Underfloor heating can shorten the drying time with a controlled heat-up protocol.
Does screed always have to lie on insulation?
Floating screed lies on a separating or insulation layer and has no direct contact with the structural floor slab. This is standard in residential rooms for sound insulation (impact sound) and thermal insulation. Bonded screed is glued directly to the structural slab – only in special cases (e.g. garages, industrial floors). Heating screed on insulation is mandatory with underfloor heating. The installation method also determines the minimum thickness and stability.