Floor Screed Calculator

How it works

screed volume = area × thickness × (1 + waste) · dry volume = screed volume × 1.27 · cement = dry volume ÷ (1 + n) × 1,440 kg/m³ · sand = dry volume × n ÷ (1 + n) · drying ≈ 1 day per mm up to 40 mm, then 2 days per extra mm

A sand–cement screed (contrapiso, solera, recrecido) is a semi-dry 1:3 to 1:5 mix laid 25–100 mm thick to give a flat base for tiles, timber or vinyl. The finished volume is the area times the thickness plus waste; the 1.27 factor gives the loose dry materials, which are split by the mix ratio and converted with cement at 1,440 kg/m³. BS 8204 recommends at least 25 mm bonded, 50 mm unbonded and 65 mm floating (65–75 mm over underfloor heating). The common drying rule — one day per millimetre for the first 40 mm and two days per millimetre beyond — is only a guide; check moisture before laying floor coverings.

Worked example

A 40 m² floor with a 50 mm screed in 1:4 and 10% waste: volume = 40 × 0.05 × 1.1 = 2.2 m³; dry volume = 2.2 × 1.27 = 2.794 m³. Cement = 2.794 ÷ 5 × 1,440 = 805 kg → 16.1, so 17 bags of 50 kg; sand = 2.794 × 4 ÷ 5 = 2.24 m³. The screed weighs about 105 kg/m² and needs roughly 40 + 2 × 10 = 60 days to dry.

Sources: BS 8204-1 Screeds, bases and in situ floorings — guidance summary (Concrete Society) · The Concrete Centre — Screeds

Frequently asked questions