How thick should floor screed be?

Traditional sand and cement screed (also known as floor screed or sand-cement screed) should be a minimum of 65mm thick when laid unbonded over insulation, or 50mm when bonded directly to a concrete slab. For underfloor heating systems, 50mm minimum above the pipes is standard — use our Underfloor Heating Coverage Calculator (/flooring/underfloor-heating-coverage-calculator) to size your UFH system. Self-levelling screed can be thinner at 25-50mm; see our Self-Levelling Compound Calculator (/flooring/self-levelling-compound-calculator) for bag quantities. Always check Building Regulations Approved Document C for your specific application.

What is the correct mix ratio for floor screed?

The standard mix for traditional floor screed is 1 part cement to 3-4 parts sharp sand (by volume). A 1:4 mix is most common for general domestic use. For heavier-duty areas like garages, a stronger 1:3 mix is recommended. The sand must be sharp (concreting) sand, not building sand, to achieve the correct strength. This calculator covers traditional, self-levelling and fast-set floor screed mixes used across UK domestic and commercial projects.

How long does screed take to dry before tiling?

As a general rule, traditional sand and cement screed takes 1 day per mm of thickness to dry sufficiently for tiling — so 65mm screed needs approximately 65 days. Self-levelling/liquid screed dries faster, typically 1 day per 2mm. Fast-set screed can be walked on in hours and tiled within days. Once dry, use our Floor Tile Calculator (/flooring/floor-tile-calculator) to work out tile quantities, or our Floor Levelling Calculator (/flooring/floor-levelling-calculator) if the screed needs a levelling skim before tiling.

How much sand do I need per m³ of screed?

For a 1:4 mix, you need approximately 1.28 tonnes of sharp sand per m³ of screed (0.8 m³ of sand at 1.6 tonnes per m³). A standard bulk bag (tonne bag) of sharp sand typically contains 0.85-0.9 m³. For a typical room (4m × 5m at 65mm depth), you would need approximately 1.7 tonnes of sand. This screed quantity calculator rounds all material quantities up so you always order enough.

Can I screed over underfloor heating pipes?

Yes, screeding over underfloor heating (UFH) is standard practice. Use a minimum 50mm screed depth above the top of the pipes for traditional screed, or 25-30mm for self-levelling liquid screed. The underfloor heating must be pressure tested before screeding. Do not turn on the heating for at least 21 days after laying traditional screed. Size your UFH system first using our Underfloor Heating Coverage Calculator (/flooring/underfloor-heating-coverage-calculator).

Screed Calculator — Sand & Cement Quantities for Floor Screeding UK

Screed Calculator — Sand, Cement & Volume for Floor Screeding

Calculate screed volume and sand/cement quantities for traditional, self-levelling or fast-set floor screed. Uses UK standard product sizes.

Floor Length

Floor Width

Screed Type

Screed Depth

65mm standard for floating, 50mm for bonded/UFH

Include wastage allowance

Adds 10% extra for compaction and losses

Wastage Percentage

10% recommended for most screed work

Price Per Tonne of Sand (optional)

Sharp sand price per tonne

Price Per Bag of Cement (optional)

25kg cement bag price

How We Calculate This

Our screed calculator works by calculating the total volume of screed needed based on your floor dimensions and desired depth, then determining the quantities of sand and cement required for your chosen mix ratio.

The formula

Volume (m³) = Length (m) × Width (m) × Depth (mm) ÷ 1000

For a traditional 1:4 mix (cement:sand), from each m³ of screed:

Sand: 0.8 m³ × 1.6 t/m³ = 1.28 tonnes of sharp sand
Cement: 0.2 m³ × 1440 kg/m³ = 288 kg = approximately 12 × 25kg bags

UK screed depth guidelines

Bonded screed: 25-40mm minimum
Unbonded screed: 50mm minimum
Floating screed (over insulation): 65mm minimum
Over underfloor heating: 50mm above pipe tops

Sand quantities are based on sharp (concreting) sand at 1.6 tonnes per m³. Cement is calculated using standard 25kg bags (available at Screwfix, Travis Perkins, Jewson and all UK builders merchants). The 10% wastage factor accounts for compaction and normal losses.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Screed Calculator — Sand, Cement & Volume for Floor Screeding

How We Calculate This

The formula

UK screed depth guidelines

Frequently Asked Questions

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Underfloor Heating Coverage Calculator