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Concrete & screed · sand · cement
How much sand and cement for a floor screed?
Sand and cement screed to a finished depth, hand-mixed or bought in. 4:1 sharp sand to cement is the normal traditional screed; the old sheet ran 8:1 on ballast for a thicker oversite screed.
1
Measure it
Every box has its own unit next to it.
Change the unit beside any box and the number converts. The (i) beside each question says what the box wants and where the figure usually comes from. Anything marked per cent is a percentage of the quantity above it.
2
Check the rates
Rates and assumptions used
These are the figures the calculator works to. Change any of them and the order list updates — your merchant’s pack sizes and your own waste allowances beat the defaults every time.
How this one works
Volume = area × depth × (1 + waste %)
Dry volume = wet × 1.5, then split by the mix ratio and converted to weight
Cement = sand weight ÷ ratio
The figures the calculator works to. Every one can be changed in step 2, and your merchant’s pack sizes and your own waste allowances beat these defaults every time.
Rate
Default
Why
Sand density
1.6 t/m³
Sharp sand, loose.
Dry-to-wet factor
1.5
Cement bag
25 kg
Sand bulk bag
0.85 t
Fibres
0.9 kg/m³
Polypropylene fibres, optional but cheap insurance against cracking.
A worked example
With the defaults the page opens on:
How long is the room? 9 metres
How wide is it? 7 metres
How deep is the screed? 75 millimetres
Which mix? 4:1 — traditional screed
Spare for waste 5 per cent
Screed
Area: 63 m²
Depth: 75 mm
Volume: 4.96 m³ — +5% waste
Sharp sand: 1.16 t— mix 4:1
Sand bulk bags: 2 bags — 1.2 / 0.85 tonnes a bag
Cement: 12 bags— 290 kg
Fibres: 4.5 kg — optional, at 0.9 kg/m³
Or ready-mixed screed: 5 m³ — if you are buying it in
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
How much sand and cement for a floor screed?
Volume × 1.5 for the dry materials, split by the mix ratio. A 9 m × 7 m room at 75 mm and 4:1 needs about 6 t of sharp sand and 60 bags of cement with 5% waste - the page shows the exact figures for your sizes.
What mix is a traditional screed?
4:1 sharp sand to cement by volume. 3:1 for a strong or thin bed, 5:1 for a floating screed over insulation.
How thick should a screed be?
75 mm unbonded, 65 mm floating over insulation, 40-50 mm bonded. Under 40 mm the calculator flags that a sand and cement mix is not the right material.
Should I add fibres?
Optional, cheap insurance against cracking: the calculator allows 0.9 kg of polypropylene fibres per cubic metre.
Read before you order. These work out quantities, not structural design — spans, lintels, rebar and foundation depths need an engineer and Building Control sign-off. Waste allowances are defaults, not promises: awkward cuts, long runs and bad weather all eat more than 5%. Where a merchant sells whole packs, the figure is rounded up to whole packs.
