A floor screed calculator determines sand-cement or self-levelling screed volumes for floor finishes over concrete slabs, underfloor heating, and insulation. This 2026 calculator provides accurate material quantities compliant with BS 8204 floor screeds and in-situ floorings standards for UK construction.
Screed provides a smooth, level surface for final floor coverings (tiles, vinyl, carpet, wood). Typical screed depths range from 25mm for bonded screeds to 65-75mm for unbonded/floating screeds. Proper screed thickness ensures structural integrity, prevents cracking, and accommodates underfloor heating systems per NHBC Standards 2026.
🔨 Floor Screed Calculator
Calculate screed volume, materials and costs
Floor Dimensions
Screed Specification
Total Screed Volume
0 m³
Including 5% wastage allowance
Material Quantities
Floor Area
0 m²
Sharp Sand Required
0 m³
Cement Bags (25kg)
0 bags
Screed Weight
0 tonnes
Screed Specifications
Screed TypeUnbonded Screed
Mix Ratio4:1 (Sand:Cement)
Coverage24 m² per m³ at 65mm
Drying Time1 day per mm up to 50mm
Traffic Use24-48 hours light traffic
Cost Estimate 2026
Sharp Sand£0
Cement£0
Additives & Fibres£0
Labour & Installation£0
Total Project Cost£0
Cost per m²£0/m²
Screed Depth Requirements 2026
Screed depth depends on screed type and floor construction. BS 8204-1:2003 specifies minimum thicknesses for different screed applications. Insufficient depth causes cracking, curling, and failure. Excessive depth wastes materials and increases drying time.
Minimum Screed Depths by Type
Screed Type
Minimum Depth
Standard Depth
Drying Time
Bonded (Direct to concrete)
25mm
40mm
25-40 days
Unbonded (On DPM/membrane)
50mm
65mm
50-65 days
Floating (On insulation)
65mm
75mm
65-75 days
Underfloor Heating (UFH)
65mm total (25mm over pipes)
75mm
65-75 days
Self-Levelling Compound
3mm
5-10mm
24-48 hours
Anhydrite Liquid Screed
35mm (UFH: 25mm over pipes)
40-50mm
Faster than sand:cement
Bonded Screed
Minimum25mm
Standard40mm
Drying25-40 days
Unbonded Screed
Minimum50mm
Standard65mm
Drying50-65 days
Floating Screed (UFH)
Minimum65mm
Standard75mm
Drying65-75 days
Types of Floor Screed
Screed selection depends on substrate condition, insulation requirements, underfloor heating, and drying time constraints. Each screed type has specific advantages, limitations, and installation requirements.
Bonded Screed
Application: Applied directly to concrete slab with bonding agent
Disadvantages: Slight cost increase (£2-4/m²), requires good mixing
Screed Mix Ratios & Materials
Traditional sand:cement screed uses 4:1 ratio (4 parts sharp sand to 1 part cement by volume). Correct mixing ensures workability, strength, and durability. BS 8204 specifies minimum 15 N/mm² compressive strength for floor screeds.
✅ Standard Screed Mix Specifications:
Mix Ratio: 4:1 (sharp sand:cement) by volume - most common domestic application
Sharp Sand: Well-graded, washed, free from clay and organic matter
Cement: Ordinary Portland Cement (OPC) or rapid-hardening cement
Water: Clean, potable water - approximately 0.4-0.5 water:cement ratio
Fibres: 0.9-1.8 kg/m³ polypropylene fibres for crack control
Strength: Minimum 15 N/mm² at 28 days (typical 20-25 N/mm²)
Screed Material Quantities
Accurate material calculation prevents shortages during installation and reduces waste. Screed volume depends on floor area and depth. Mix ratios determine sand and cement quantities.
📐 Material Calculation Formulas:
Screed Volume: Area (m²) × Depth (m) = Volume (m³)
Coverage: 1 m³ mixed screed covers approximately 15.4 m² at 65mm depth
Screed Drying Times 2026
Screed must dry sufficiently before applying floor finishes. Moisture trapped beneath impermeable coverings (vinyl, tiles) causes adhesive failure, mould, and floor damage. BS 8203 specifies moisture testing requirements before flooring installation.
⚠️ Screed Drying Time Guidelines:
General Rule: 1 day per mm thickness up to 50mm, then additional time (e.g., 65mm = 75-80 days)
Bonded Screed (40mm): 40-50 days minimum in good conditions
Unbonded Screed (65mm): 75-85 days minimum
Floating Screed (75mm): 90-100 days minimum
Rapid-Dry Screed: 14-21 days with additives (higher cost)
Liquid Screed: Faster drying than traditional (50-70% quicker in some cases)
Moisture Testing: Use hygrometer or carbide bomb test - max 75% RH for most finishes
Forced Drying: Heating/dehumidification accelerates drying but requires gradual increase (not before 7 days)
Screed Installation Process
Proper installation ensures flat, level, crack-free floors. Professional screeding requires skill, correct tools, and attention to detail. DIY feasible for small areas with experience.
1. Preparation
Substrate: Clean, free from dust, oil, laitance
Bonded: Apply SBR bonding agent or cement slurry
Unbonded: Lay 1200 gauge DPM, 150mm laps, turned up at edges
Datum Level: Establish level using laser or spirit level
Screeding Rails: Fix timber or metal rails at correct height
Bay Sizes: Maximum 4-5m bays, avoid continuous large areas
Perimeter Strips: 10mm foam strips against walls for movement
3. Mixing & Laying
Mix Quality: Consistent, not too wet (crumbly texture)
Application: Spread between rails, compact thoroughly
Screeding: Straight edge pulled across rails, remove voids
Finishing: Wood float for smooth finish, avoid over-trowelling
4. Curing
Protection: Cover with polythene 24 hours after laying
Curing Time: Keep polythene on for 7 days minimum
Temperature: Maintain 10-20°C, protect from frost and direct sun
Traffic: Light foot traffic after 48 hours, avoid loading
Screed Costs 2026
Screed costs include materials (sand, cement, additives), labour, equipment hire, and drying time considerations. Professional installation recommended for quality and warranty. Liquid screed more expensive than traditional but saves time and allows thinner depths.
Screed Cost Comparison (Per m²)
Screed Type
Materials
Labour
Total Cost
Traditional Sand:Cement (65mm)
£8-12/m²
£12-18/m²
£20-30/m²
Fibre-Reinforced (65mm)
£10-14/m²
£12-18/m²
£22-32/m²
Rapid-Dry Screed (65mm)
£15-20/m²
£12-18/m²
£27-38/m²
Liquid Anhydrite Screed (40mm)
£18-24/m²
£8-12/m²
£26-36/m²
Self-Levelling Compound (5-10mm)
£15-25/m²
£8-15/m²
£23-40/m²
Traditional Sand:Cement
Materials£8-12/m²
Labour£12-18/m²
Total£20-30/m²
Fibre-Reinforced
Materials£10-14/m²
Labour£12-18/m²
Total£22-32/m²
Liquid Anhydrite
Materials£18-24/m²
Labour£8-12/m²
Total£26-36/m²
Floor Screed Calculator FAQs
How much screed do I need for my floor?
Calculate: Floor Area (m²) × Depth (m) = Volume (m³). Example: 24m² floor at 65mm depth = 24 × 0.065 = 1.56 m³. Add 5% wastage = 1.64 m³. For materials: 4:1 mix uses approximately 1.3 m³ sand and 18 bags cement (25kg) per 1.64 m³ screed. Coverage: 1 m³ covers 15.4 m² at 65mm depth.
What depth should floor screed be?
Depends on screed type: Bonded screed minimum 25mm (standard 40mm), Unbonded screed minimum 50mm (standard 65mm), Floating screed minimum 65mm (standard 75mm). Underfloor heating requires 65-75mm total with 25mm minimum cover over pipes. Insufficient depth causes cracking and failure. Self-levelling compounds typically 3-10mm. Always follow BS 8204 standards.
How long does screed take to dry?
Rule of thumb: 1 day per mm up to 50mm. 65mm unbonded screed takes 75-85 days to dry sufficiently for most floor finishes. 40mm bonded screed takes 40-50 days. Drying time depends on temperature, humidity, ventilation. Rapid-dry screeds reduce time to 14-21 days. Always moisture test before laying impermeable finishes (vinyl, tiles). Premature covering causes adhesive failure and mould.
What is the mix ratio for floor screed?
Standard mix is 4:1 (4 parts sharp sand to 1 part cement) by volume. For 1m³ screed: use approximately 0.8m³ sharp sand (1280 kg) and 0.32m³ cement (450 kg or 18 bags of 25kg). Add plasticiser as per manufacturer instructions. Stronger mixes like 3:1 used for heavy-duty applications. Mix should be crumbly, not wet - squeeze test: holds shape then crumbles.
Can I lay screed myself?
DIY possible for small rooms (under 20m²) with experience. Challenges: achieving consistent level, correct mix consistency, working within pot life, proper compaction, avoiding surface defects. Requires: laser level, screeding rails, straight edge, mixing equipment, materials. Professional screeding recommended for: large areas, underfloor heating, critical levels, warranty requirements. Poor screeding causes costly remedial work and floor finish failures.
How much does floor screed cost in 2026?
Traditional sand:cement screed (65mm) costs £20-30 per m² installed (2026 prices). Materials £8-12/m², labour £12-18/m². Typical room 20m² costs £400-600. Liquid anhydrite screed £26-36/m² (faster drying, thinner). Self-levelling compound £23-40/m² for thin applications. Add insulation costs (£12-20/m²) if required for floating screed. Prices vary by location and project size.
What is the difference between bonded and unbonded screed?
Bonded screed: Applied directly to concrete with bonding agent, 25-40mm thick, strong bond but prone to cracking if debonds. Unbonded screed: Laid on DPM/membrane, 50-65mm minimum, independent movement, moisture barrier, more crack-resistant. Floating screed: On insulation, 65-75mm minimum, provides thermal/acoustic benefits. Choice depends on floor construction, insulation needs, and underfloor heating requirements. BS 8204 specifies minimum thicknesses.
Do I need fibres in floor screed?
Recommended but not always essential. Polypropylene fibres (0.9-1.8 kg/m³) improve crack resistance, reduce curling, increase tensile strength. Particularly beneficial for: unbonded/floating screeds, large bay areas, fast-drying conditions, underfloor heating. Cost addition £2-4/m². Steel fibres used for heavy industrial applications. Most modern screeds include fibres as standard. Mix thoroughly to distribute evenly - poor distribution reduces effectiveness.
Can you screed over underfloor heating?
Yes, screed is ideal for underfloor heating. Minimum 65-75mm total depth with 25mm minimum cover over UFH pipes. Use floating screed construction on insulation. Liquid anhydrite screed excellent for UFH - better thermal conductivity, flows around pipes, allows thinner 35-40mm total. Commission heating system carefully - gradual warm-up after minimum 7-21 days depending on screed type. Never switch on heating during initial curing period.
Why has my screed cracked?
Common causes: Too thin (below minimum depths), Excess water in mix (weak screed), Rapid drying (no curing protection), No movement joints (large bay areas), Poor substrate preparation (debonding), Premature loading or heating. Prevention: Follow minimum depths per BS 8204, Use correct mix (not too wet), Cover with polythene for 7 days, Limit bay sizes to 4-5m with movement joints, Proper substrate prep and bonding, Allow full curing before loading. Minor hairline cracks cosmetic; structural cracks require repair.
