Floor screed calculator — cement bags and sand, worked out
A 50 m² floor screeded 50 mm thick in a standard 1:4 mix, with 10% waste, takes 21 bags of cement and about 4.58 tonnes of sand. Enter your own area, thickness and mix below — metric only, free, no signup.
Your quantities
How the cement and sand are worked out
The calculator starts from the laid (wet) volume: your area multiplied by the screed thickness, with your waste percentage added — you always batch a little more than the floor swallows. It then converts to dry volume with the standard factor of 1.30, because loose dry cement and sand compact by roughly that much once they are mixed and laid.
The dry volume is split by your mix ratio: in a 1:4 mix, cement takes one part in five and sand four parts in five. Cement is weighed at the standard bulk density of 1,440 kg per m³ and rounded up to whole 50 kg bags; sand is weighed at 1,600 kg per m³ and shown in tonnes. Change the mix and the cement count moves with it — a richer 1:3 mix for a hard-wearing floor carries noticeably more cement than a lean 1:5 levelling mix.
How the screed is built changes what the number means. A bonded screed is laid directly on the slab and can run thinner; an unbonded screed sits on a separating membrane, and a floating screed rides on insulation boards — both need more depth to carry load without cracking, and both belong in the thickness you enter. In wet areas the floor also falls toward the drain, so the depth at the door and the depth at the drain are two different numbers.
Running these jobs? Tiling & Flooring
How to use the screed calculator
- Measure the floor: length × width in metres, one rectangle per room or zone.
- Set the screed thickness in millimetres — 50 mm is a common floating screed over insulation or a slab; thin bonded screeds run less.
- Choose the mix: 1:4 is the standard floor mix; 1:3 for heavy wear and external work; 1:5 for light domestic levelling.
- Set the waste — 10% covers spillage, uneven slabs and the last part-batch.
- Read the order list: cement in kilos and 50 kg bags, sand in cubic metres and tonnes.
How much cement and sand for a 50 m² floor at 50 mm?
The laid volume is 50 × 0.05 = 2.5 m³, and 10% waste for batching brings the mix to 2.75 m³. Converted to dry materials at the 1.30 factor, that is 3.575 m³ to order and mix.
At 1:4, cement takes one fifth of the dry volume: 0.715 m³, which at 1,440 kg per m³ is 1,029.6 kg — 21 bags of 50 kg, rounded up. Sand takes the other four fifths: 2.86 m³, about 4.58 tonnes at 1,600 kg per m³.
A second shape: a floating screed over insulation in a 24 m² room, laid 65 mm thick at a richer 1:3 mix with the same 10% waste. The laid volume is 24 × 0.065 = 1.56 m³, or 1.716 m³ with waste; dry, that is 2.23 m³. Cement takes a quarter of the dry volume at 1:3 — 0.558 m³, about 803 kg, so 17 bags — and sand the remaining three quarters: 1.67 m³, about 2.68 tonnes. Same floor area as a thin bonded job, a very different order: thickness and mix are where the money sits.
Screed mixes and assumptions the calculator uses
Which mix for which floor
| Mix (cement : sand) | Typical use |
|---|---|
| 1 : 3 | Heavy wear — workshops, external yards, industrial floors |
| 1 : 4 | The standard floor screed — under tiles, stone and most finishes |
| 1 : 5 | Light domestic levelling under floating floors |
Assumptions, stated
| Assumption | Value used |
|---|---|
| Dry-volume factor | 1.30 × the laid (wet) volume |
| Cement density | 1,440 kg per m³, in 50 kg bags |
| Sand density | 1,600 kg per m³ |
Screed habits that save a floor
- Measure the slab's low spots before you fix the thickness — an uneven slab eats screed, and the average depth is what belongs in the calculator.
- Batch the whole room in one consistency of mix; changing the water or the ratio mid-floor shows up as weak patches later.
- Let the screed cure before tiles or stone go down — a floor finish laid on green screed is a callback waiting to happen.
- On big floors, order sand by the tonne against the calculator's figure and keep the bags dry; wet cement bags go off before they ever reach the mixer.
- In wet areas, measure the depth at the door and at the drain and enter the average — the fall between them is screed too, and it is the half of the room everyone forgets to batch for.
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How thick should a floor screed be?+
It depends on the build-up: a bonded screed can be thin, an unbonded or floating screed over insulation is commonly around 50 mm or more, and the specification for the job governs. The calculator takes any thickness you enter — what matters is that the number is the job's real average depth.
Does the calculator include labour or ready-mix prices?+
No — quantities only, like every tool here. It counts cement bags and sand tonnage; what they cost this week from your supplier, and what your crew charges to lay them, belongs in your own price book.
Why is there no imperial switch?+
Screed in the Gulf is specified in millimetres and square metres, so the calculator is metric only. If your drawing is in feet, multiply square feet by 0.0929 to get square metres and inches by 25.4 to get millimetres.
What about fibre or additives in the screed?+
They change the specification, not the bulk quantities — the cement and sand volumes here stay the base order, and fibres or admixtures are added per the manufacturer's dosage on top.
How long before tiles can go down on new screed?+
As a rule of thumb, allow about a day of drying per millimetre of thickness for the first 40 mm, and longer beyond that — but it is only a rule of thumb. Cement screeds hold moisture deep inside, and a floor finish laid too early traps it. Check the adhesive and screed manufacturers' guidance, and test the moisture where the finish matters; the calendar alone does not clear a floor.