Floor screed calculator – bags per m² and drying time
How much sand-cement screed you need per m² for any thickness, how many 25 kg bags, drying time per cm and the moisture limits before laying floors.
Dry screed mix ≈ 20 kg per m² for every 1 cm of thickness · bags = area × thickness (cm) × 20 ÷ 25
| Area × thickness | Dry mix | 25 kg bags |
|---|---|---|
| 20 m² × 5 cm | 2,000 kg | 80 |
| 12 m² × 6.5 cm (underfloor heating) | 1,560 kg | 63 |
| 200 sq ft (18.6 m²) × 2 in (5 cm) | 1,860 kg | 75 |
Floating screed on insulation is usually 5–6 cm (at least 4.5 cm over heating pipes). Add 3–5 % for waste.
Drying time (sand-cement, about 20 °C)
- Up to 4 cm: roughly 1 week per cm.
- 5 cm: about 6–8 weeks; 6–7 cm: 10 weeks or more.
- Protect from draughts, sun and frost for the first 3–7 days.
Moisture before laying floors
Common limits (CM method): cement screed ≤ 2.0 % (≤ 1.8 % with underfloor heating), anhydrite ≤ 0.5 % (≤ 0.3 %). In the US, flooring makers usually specify the RH test (ASTM F2170) instead – follow the flooring manufacturer.
Ask AI Onin for your own numbersAI Onin is an AI assistant for construction: material quantities, cost estimates in your currency, bill of quantities checks and site photo analysis. Values are typical and approximate – follow the manufacturer's data sheet, your local code and your engineer.