Screed Calculator

Written byOleh Soloninupdated 25 September 2026

Floor area, m²

Layer thickness, mm

Bag weight, kg

Case under SP 29.13330

It sets the smallest thickness allowed by clause 8.2 of the Russian floor code.

Advanced options

Mix density, kg/m³

From the bag: the amount of mix follows it directly.

Spare, %

Result

Volume, m³0.875
Mass of mix, kg1,575
Bags63
With spare67
Smallest thickness in the code
20 mm on a floor slab (SP 29.13330.2011, clause 8.2, for a screed that creates a slope)
Your thickness50 mm is at or above the minimum
Strength over time
After 7 days the bond strength must reach at least 50% of the design value, and the design strength is specified at 28 days (SP 29.13330.2011, clause 8.8)
How it was calculated
17.5 m² × 50 mm ÷ 1000 = 0.875 m³ 0.875 × 1,800 kg/m³ = 1,575 kg of mix 1,575 ÷ 25 kg = 63 bags, 67 with a 5% allowance

Counts the material and checks the thickness

Mix volume and mass, bags with an allowance, and your thickness checked against the SP 29.13330.2011 minimum.

Screed mix follows the volume of the layer: 17.5 m² at 50 mm is 0.875 m³, and at a density of 1,800 kg/m³ that is 1,575 kg — 63 bags of 25 kg. A 5% allowance adds four more bags.

The thickness, though, is not a free choice. Russian code SP 29.13330.2011 sets minimum values, and they depend on what the screed sits on: a floor slab, a thermal or acoustic layer, or pipework.

How to use

Enter the floor area and the thickness of the layer in millimetres.
Take the density of the mix and the bag weight from the bag — the number of bags follows them directly.
Pick the case from SP 29.13330 and, for a screed over pipes, the pipe diameter; the calculator compares your thickness with the minimum.

Bags of mix by area and thickness

Every row is a separate run of this calculator at a density of 1,800 kg/m³ with a 5% allowance.

Every value was produced by the calculator on this page.
Area	Thickness	Volume	Mass	Bags	With allowance	Bag
17.5 m²	50 mm	0.875 m³	1,575 kg	63	67	25 kg
30 m²	40 mm	1.2 m³	2,160 kg	87	91	25 kg
20 m²	70 mm	1.4 m³	2,520 kg	51	53	50 kg
17.5 m²	30 mm	0.525 m³	945 kg	38	40	25 kg
20 m²	50 mm	1 m³	1,800 kg	72	76	25 kg

What SP 29.13330.2011 requires

Clause 8.2 gives the smallest thickness for a cement-sand or concrete screed laid to create a fall: 20 mm on floor slabs and 40 mm over a thermal or acoustic layer. A screed covering pipework, underfloor heating included, must be at least 45 mm thicker than the pipe diameter — 61 mm for a 16 mm pipe.

Clause 8.9 adds the case of point loads: above 20 kN the thickness of a screed over insulation is set by calculation, but never less than 100 mm and in concrete of class B22.5 or better. This is the Russian rule; if you build elsewhere, treat the numbers as a sanity check against your own code.

Not "how long it dries" but "when it has gained strength"

The code sets strength, not a drying time. Clause 8.8 requires a bond strength of at least 0.6 MPa to the concrete base at 28 days, and at 7 days its bond to the base must have reached at least 50% of the design value.

That is why this calculator no longer prints "days to dry": the figure depends on the mix, the thickness and the temperature and humidity of the room, and the manufacturer states it for their product. What can be checked is strength and the residual moisture of the base before the floor covering goes down.

What this calculator shows

Volume and mass of mix, bag count and a figure with spare
The SP 29.13330.2011 minimum thickness for the case you pick, compared with yours

What to keep in mind

Mix density defaults to 1,800 kg/m³; take the density of your own mix from the bag.
Water and drying time are not calculated: the water comes from the bag's instructions, and a base is ready when its strength and residual moisture say so.

FAQs

How many bags of screed for 20 m²?

At 50 mm and 1,800 kg/m³ that is 1 m³ and 1,800 kg: 72 bags of 25 kg, or 76 with a 5% allowance. In 50 kg bags it is half as many pieces.

What is the minimum screed thickness?

Under clause 8.2 of SP 29.13330.2011, for a screed laid to create a fall: 20 mm on a floor slab and 40 mm over a thermal or acoustic layer. Over pipes it is the pipe diameter plus 45 mm.

How thick above underfloor heating pipes?

At least 45 mm more than the pipe diameter: 61 mm for a 16 mm pipe, 65 mm for a 20 mm one. Pick the pipework case and the calculator applies that rule.

How long does screed take to dry?

The code does not say. It sets bond strength instead — at least 0.6 MPa to the concrete base at 28 days and at least 50% of the design bond at 7. When a covering can go down depends on the manufacturer's data and on the residual moisture of the base.

How much water per bag?

Whatever the bag says: a sand-cement screed, a semi-dry mix and a self-levelling compound all take different amounts. The calculator gives the dry mass and leaves the water to the instructions.

Why does the calculator ask for the density?

It turns the volume of the layer into kilograms. At 1,800 kg/m³ a cubic metre weighs 1,800 kg; at 1,600 it weighs two hundred kilograms less, which changes the number of bags by roughly a tenth. The figure is on the bag.

Worked example

A 17.5 m² room, 50 mm layer

Input: 17.5 m², 50 mm, density 1,800 kg/m³, 25 kg bags

Output: 0.875 m³, 1,575 kg, 63 bags

Note: 67 bags with a 5% allowance; 50 mm on a floor slab is above the 20 mm minimum.

Useful links

All tools in Building & Repair

Screed Calculator

Result

Related tools

Concrete Calculator

Laminate Flooring Calculator

Insulation Calculator

Useful links