Calculate Concrete Volume, Thickness & Material Costs
Accurate Slab Calculations for UK Construction Projects
A concrete slab calculator determines the volume of concrete required for ground-bearing slabs, suspended slabs, garage floors, and base slabs. Our 2026 calculator computes concrete volume in cubic metres (m³), tonnes required, reinforcement specifications, and project costs based on Building Regulations Approved Document A and BS 8500:2015 standards.
Proper slab design ensures structural integrity, prevents cracking, and complies with NHBC Standards 2026. Typical residential slabs range from 100mm for light-duty applications to 150-200mm for domestic floors, with heavier industrial slabs requiring 200-300mm+ thickness plus appropriate reinforcement.
🏗️ Concrete Slab Calculator
Calculate concrete volume, reinforcement and costs
Slab Dimensions
Concrete Volume Required
0 m³
Including wastage allowance
Material Quantities
Slab Area
0 m²
Concrete Tonnes
0 tonnes
Ready-Mix Loads
0 loads
DPM Required
0 m²
Reinforcement Details
Mesh TypeA193 Mesh
Mesh Sheets Required0 sheets
Mesh Coverage4.8m x 2.4m per sheet
Spacers/ChairsRequired - 4 per m²
Cost Estimate 2026
Concrete Cost£0
Reinforcement Cost£0
DPM + Insulation£0
Labour (Estimate)£0
Total Project Cost£0
Concrete Slab Thickness Requirements 2026
Slab thickness depends on the intended use, expected loads, ground conditions, and reinforcement. UK Building Regulations Part A and NHBC Chapter 5.1 provide minimum thickness standards for domestic and commercial applications.
Standard Slab Thicknesses by Application
Application
Minimum Thickness
Concrete Grade
Reinforcement
Garden Shed Base
75-100mm
C20/25 (GEN3)
Not required
Garage Floor (Domestic)
100-125mm
C25/30 (RC25)
A142 or A193 mesh
House Ground Floor
150mm
C25/30 (RC25)
A193 mesh
Suspended Floor Slab
150-200mm
C28/35 (RC28)
A252 or A393 mesh
Driveway (Cars only)
100-125mm
C25/30 (RC25)
A193 mesh
Commercial Light Use
150-200mm
C28/35 (RC28)
A252 or A393 mesh
Commercial Heavy Use
200-250mm
C32/40 (RC32)
A393 mesh or bars
Industrial / Warehouse
250-300mm+
C32/40 - C40/50
Bar reinforcement + design
Garden Shed Base
Thickness75-100mm
Concrete GradeC20/25 (GEN3)
ReinforcementNot required
House Ground Floor
Thickness150mm
Concrete GradeC25/30 (RC25)
ReinforcementA193 mesh
Commercial Heavy Use
Thickness200-250mm
Concrete GradeC32/40 (RC32)
ReinforcementA393 mesh or bars
Reinforcement Mesh Specifications
Steel reinforcement mesh controls cracking and distributes loads across the slab. Mesh is designated by cross-sectional area per metre width. BS 4449:2005 specifies reinforcement standards. Mesh should be positioned mid-depth in the slab using plastic spacers or chairs.
Positioning: Place mesh at mid-depth (half the slab thickness) using 50mm spacers or chairs
Overlap: Minimum 300mm overlap between mesh sheets, or 2 squares of mesh pattern
Edge Distance: Maintain 50mm minimum cover from slab edges
Tie Wire: Secure overlaps with 1.6mm binding wire at 400mm centres
Sheet Size: Standard mesh sheets are 4.8m x 2.4m (11.52m² coverage)
Ground-Bearing Slab Construction Layers
A properly constructed ground-bearing slab includes multiple layers beneath the concrete to prevent moisture ingress, provide insulation, and create a stable base. Approved Document C (Site preparation and resistance to contaminants) and Part L (Conservation of fuel and power) specify layer requirements.
✅ Standard Ground-Bearing Slab Build-Up (Bottom to Top):
8. Floor Finish: Screed, tiles, vinyl, or other flooring as required
Concrete Grades and Specifications
Concrete grade selection depends on slab application and structural requirements. UK standards use C (cylinder strength) designations per BS 8500. Higher grades provide greater compressive strength but cost more.
Concrete Grade Specifications 2026
Grade
Strength (N/mm²)
Applications
Cost per m³
C20/25 (GEN3)
20 N/mm²
Kerbs, foundations, non-structural slabs
£95-110
C25/30 (RC25)
25 N/mm²
Domestic floors, driveways, garages
£100-120
C28/35 (RC28)
28 N/mm²
Suspended slabs, light commercial
£105-125
C32/40 (RC32)
32 N/mm²
Heavy commercial, industrial floors
£110-130
C40/50 (RC40)
40 N/mm²
Heavy industrial, precast beams
£120-145
C20/25 (GEN3)
Strength20 N/mm²
UseNon-structural
Cost per m³£95-110
C25/30 (RC25)
Strength25 N/mm²
UseDomestic floors
Cost per m³£100-120
C32/40 (RC32)
Strength32 N/mm²
UseHeavy commercial
Cost per m³£110-130
Concrete Slab Costs 2026
Total slab costs include materials (concrete, reinforcement, DPM, insulation), labour, plant hire, and site preparation. Costs vary by location, accessibility, project size, and specification. Larger pours benefit from economies of scale.
⚠️ Typical Cost Breakdown (150mm Domestic Slab, per m²):
Concrete (C25/30): £15-18 per m² (0.15m³ @ £100-120/m³)
Reinforcement (A193 mesh): £2-3 per m²
DPM (1200 gauge): £1-2 per m²
Insulation (100mm): £8-12 per m² (if required for Part L)
Hardcore & Preparation: £5-8 per m²
Labour: £12-18 per m² (excavation, pour, finish)
Total Material & Labour: £43-61 per m² (excluding insulation)
With Insulation: £51-73 per m² total
Professional Requirements and Building Control
Most domestic ground-bearing slabs require Building Control approval under Part A (Structure), Part C (Site preparation), and Part L (Insulation). Notify Building Control before work commences. Inspections are required at foundation trenches, DPM installation, and before concrete pour.
When Building Control Required
New house floors: Always required
Extensions: Required if habitable space
Garage attached to house: Required
Suspended slabs: Always require approval
Commercial buildings: Always required
When Building Control NOT Required
Detached garage < 30m²: No heating, >1m from boundary
Garden shed: Under 15m², single storey
Patio slab: External paving, no structure above
Greenhouse: Lightweight structure under 30m²
Professional Services Costs 2026
Service
Typical Cost
Details
Building Control Fee
£300-800
Depends on project value and authority
Structural Engineer Design
£400-1200
For suspended slabs or complex designs
Ground Investigation
£500-1500
Trial pits, soil testing (if required)
Concrete Pump Hire
£200-400
Per visit, for difficult access sites
Poker Vibrator Hire
£40-80/day
For compacting concrete
Building Control Fee
Cost£300-800
DetailsProject dependent
Structural Engineer Design
Cost£400-1200
DetailsSuspended slabs
Concrete Pump Hire
Cost£200-400
DetailsPer visit
Concrete Slab Calculator FAQs
How thick should a concrete slab be for a house?
A standard domestic ground-bearing concrete floor slab should be minimum 150mm thick with A193 reinforcement mesh and C25/30 concrete grade. This complies with NHBC Standards and Building Regulations Part A. Suspended slabs may require 175-200mm thickness depending on span. Always consult structural calculations for specific requirements.
How do I calculate how much concrete I need for a slab?
Calculate concrete volume: Length (m) × Width (m) × Thickness (m) = Volume (m³). For example, a 5m × 4m slab at 150mm (0.15m) thick = 5 × 4 × 0.15 = 3.0m³. Add 10% wastage = 3.3m³ total. Ready-mix concrete is ordered in m³, with typical lorry capacity of 6-8m³.
Do I need reinforcement in a concrete slab?
Yes, most domestic slabs require reinforcement mesh. A193 mesh is standard for 150mm house floors and garage slabs. Reinforcement controls cracking, distributes loads, and is required by Building Regulations for structural slabs. Unreinforced slabs are only acceptable for light-duty applications like shed bases under 100mm thickness.
What is the cost of a concrete slab per m² in 2026?
A 150mm domestic concrete slab costs £51-73 per m² including materials and labour (2026 prices). This includes: C25/30 concrete (£15-18/m²), A193 mesh (£2-3/m²), DPM (£1-2/m²), insulation (£8-12/m²), hardcore (£5-8/m²), and labour (£12-18/m²). Larger projects achieve lower per m² costs.
Can I pour a concrete slab myself?
DIY concrete slabs are possible for small projects like shed bases or garden slabs under 10m². You'll need: proper ground preparation, DPM, reinforcement, correct concrete mix, power tools (mixer/vibrator/float), and physical capability. Larger domestic floor slabs (20m²+) should be professionally installed to ensure quality, Building Control compliance, and structural integrity. Ready-mix delivery is cost-effective for volumes over 1m³.
How long before I can walk on a new concrete slab?
Wait 24 hours before light foot traffic on fresh concrete. After 48 hours, careful walking is safe. Wait 7 days before vehicle traffic or heavy loads. Concrete reaches 75% strength at 7 days and full design strength at 28 days. Protect fresh concrete from rain, frost, and rapid drying for 3-7 days using polythene sheeting.
What is a DPM and why is it needed under a slab?
DPM (Damp Proof Membrane) is a 1200 gauge polythene sheet installed under concrete slabs to prevent ground moisture rising through the slab. Building Regulations Approved Document C requires DPM for habitable floors. DPM is lapped 150mm at joints, sealed with tape, and linked to wall DPC. Without DPM, rising damp causes condensation, mould, and flooring failure.
Do I need insulation under a concrete floor slab?
Yes, if the slab forms part of a heated building. Building Regulations Part L 2021 requires floor U-values of 0.13 W/m²K (new build) or 0.18 W/m²K (extensions). This typically requires 100-150mm rigid insulation (Kingspan/Celotex) beneath or above the slab. Unheated buildings (detached garages, sheds) don't require insulation unless specifically designed for comfort.
What happens if a concrete slab is too thin?
Thin slabs risk: cracking under load, structural failure, excessive deflection, failed Building Control inspection, inadequate load capacity, difficulty installing flooring, reduced service life. Remedial options are expensive: demolish and rebuild, overlay with new slab (if height allows), structural topping (specialist). Always follow calculated thicknesses and obtain Building Control approval.
How much hardcore do I need under a concrete slab?
Typical hardcore layer is 150-300mm compacted Type 1 MOT stone or crushed concrete. For soft or variable ground, increase to 300-450mm. Calculate volume: Area (m²) × Depth (m) = Volume (m³). A 20m² slab with 200mm hardcore needs: 20 × 0.2 = 4m³. Compact in 100mm layers using a plate compactor. Add 50mm sharp sand blinding over hardcore before DPM.
