🏗️ Concrete Slab Calculator UK
Calculate concrete volume, weight, truck loads, reinforcement mesh, sub-base depth, and estimated cost for any UK slab — floor, driveway, patio, or foundation. Free metric calculator 2026.
Concrete Slab Calculator
Select your slab type, enter dimensions, specify your mix and options — get instant volume, weight, trucks, mesh and cost estimate.
📦 Sub-Base & Blinding Options
🔩 Reinforcement Options
💷 Cost & Ordering Options
📦 Concrete Order
🔩 Reinforcement
🏗️ Sub-Base & Blinding
💷 Cost Estimate
✅ Pre-Pour Checklist
UK Concrete Slab Types — Which Do You Need?
The correct concrete slab specification depends on the intended use, loading, exposure conditions, and whether the slab is reinforced or plain. The four main UK domestic and commercial slab types are described below.
Ground-Bearing Floor Slab
The most common UK domestic slab — a reinforced concrete floor poured directly onto a compacted sub-base, DPM, and insulation. Standard specification is RC30/C at 150mm thickness with A252 fabric mesh (10mm cover to mesh). Must comply with NHBC Standards Chapter 4.2 and Approved Document C for moisture resistance.
Driveway / Hardstanding Slab
Domestic driveways and car standings require PAV1 or PAV2 mix to BS 8500 for durability against freeze-thaw and de-icing salt attack. Minimum 100mm for cars, 150mm for vans and SUVs, 175–200mm for HGVs. Always requires compacted MOT Type 1 sub-base and a DPM or sub-base membrane beneath.
Patio / Path Slab
Pedestrian-only slabs can be specified at 75–100mm using GEN3 or RC25/C mix. Always lay on a minimum 100mm compacted MOT Type 1 or sharp sand sub-base. Provide 1:60 fall away from the building for surface drainage. Movement joints at maximum 3–4m centres prevent shrinkage cracking.
A ground-bearing slab sits directly on the compacted ground — all loads transfer to the ground beneath. This calculator is designed for ground-bearing slabs. A suspended slab spans between supports (walls, beams, or columns) and is designed to Eurocode 2 (BS EN 1992-1-1) — it requires a structural engineer's design and cannot be calculated using a simple volume calculator. Suspended slabs are used where the ground is unsuitable for bearing (e.g. made ground, shrinkable clay, mineshafts) or where an underfloor void is required.
Concrete Slab Thickness Guide — UK Standards 2026
Slab thickness is the single most critical dimension — too thin and the slab will crack under load or during shrinkage; over-specified and you waste concrete and money. The table below gives UK minimum and recommended thicknesses for all common slab applications.
| Slab Application | Min Thickness | Recommended | BS 8500 Mix | Fabric Mesh | Sub-Base |
|---|---|---|---|---|---|
| Patio / garden path | 75mm | 100mm | GEN3 / RC25/C | A142 or none | 100mm MOT Type 1 |
| Domestic floor slab | 100mm (NHBC) | 150mm | RC30/C | A252 | 150mm MOT Type 1 |
| Garage floor slab | 100mm | 150mm | RC30/C | A252 | 150mm MOT Type 1 |
| Driveway — cars | 100mm | 150mm | PAV1 | A252 | 200mm MOT Type 1 |
| Driveway — vans / SUVs | 150mm | 175mm | PAV1 | A393 | 200mm MOT Type 1 |
| Commercial floor slab | 150mm | 200mm | RC35/C | A393 | 250mm MOT Type 1 |
| HGV / lorry yard | 200mm | 250mm | RC35/C | A393 T+B | 300mm MOT Type 1 |
| Industrial warehouse | 200mm | 250–300mm | RC35/C (designed) | Structural design | 300mm+ engineered |
| Raft foundation | 300mm | 350–450mm | RC30/C or designed | Structural design | 150mm blinding |
Reducing slab thickness from 150mm to 100mm saves approximately £6–10 per m² in concrete cost but doubles the risk of cracking and structural failure under normal domestic loading. Remedial work to break out and re-pour an undersized slab costs £80–150 per m² — far exceeding any saving. Always specify to NHBC and Approved Document A minimum requirements and obtain a structural engineer's approval for any deviation from standard thicknesses.
Concrete Slab Reinforcement — Fabric Mesh Reference (BS 4483)
Steel fabric reinforcement to BS 4483 is the standard reinforcement method for UK concrete slabs. Fabric mesh controls shrinkage cracking, distributes point loads, and adds structural integrity. Sheets are 4.8m × 2.4m as standard, with 300mm minimum lap at all joints per BS 8110 / Eurocode 2.
| Mesh Reference | Bar Dia (mm) | Spacing (mm) | Steel Area (mm²/m) | Weight (kg/m²) | Sheet Size | Typical Use |
|---|---|---|---|---|---|---|
| A142 | 6 | 200 × 200 | 142 | 2.22 | 4.8 × 2.4m | Patio, light domestic floor |
| A193 | 7 | 200 × 200 | 193 | 3.02 | 4.8 × 2.4m | Domestic floor slab |
| A252 ⭐ | 8 | 200 × 200 | 252 | 3.95 | 4.8 × 2.4m | Standard UK domestic slab (most common) |
| A393 | 10 | 200 × 200 | 393 | 6.16 | 4.8 × 2.4m | Driveway, garage, commercial floor |
| B196 | 7 | 100 × 200 | 252 / 126 | 3.05 | 4.8 × 2.4m | Asymmetric loading — main bars one direction |
| B503 | 8/10 | 100 × 200 | 503 / 252 | 5.93 | 4.8 × 2.4m | Commercial slab with heavy one-way loading |
| C283 | 6 | 100 × 400 | 283 / 70.8 | 2.61 | 4.8 × 2.4m | Highway long-mesh, crack control only |
The nominal cover to steel fabric mesh must be maintained throughout the pour. For RC30/C concrete in an internal domestic ground floor (Exposure Class XC1), the minimum nominal cover is 25mm to BS EN 1992-1-1. In a driveway or external slab (Exposure Class XF1 — freeze-thaw), the minimum cover increases to 35mm. Use plastic slab spacers / chairs placed at 1.0m maximum centres to maintain cover — walking on unsupported mesh before concrete is placed is the most common cause of insufficient cover on UK domestic sites.
Concrete Slab Cost Guide — UK 2026
The total cost of a concrete slab in the UK depends on concrete mix price, sub-base depth, reinforcement specification, formwork, placing and finishing labour, and regional price variation. The figures below are typical 2026 supply-and-fix costs for a contractor-installed slab including all materials and labour.
| Slab Type | Thickness | Mix | Concrete /m³ | Supply & Fix /m² | Cost Band |
|---|---|---|---|---|---|
| Patio / path | 100mm | GEN3 | £95–120 | £65–95 | Low |
| Domestic floor slab | 150mm | RC30/C | £115–145 | £90–130 | Medium |
| Garage floor slab | 150mm | RC30/C | £115–145 | £90–130 | Medium |
| Concrete driveway (cars) | 150mm | PAV1 | £115–150 | £100–145 | Medium |
| Concrete driveway (HGV) | 200mm | PAV1 | £115–150 | £130–180 | Medium–High |
| Commercial floor slab | 200mm | RC35/C | £125–165 | £130–200 | High |
| Industrial / warehouse | 250mm | RC35/C | £125–165 | £150–230 | High |
Ready-mix concrete, haulage, and groundwork labour costs in London and the South East run 20–30% above national average figures. A domestic floor slab priced at £100/m² nationally will typically cost £120–130/m² in London. Always obtain at least three quotes from local contractors and verify that each quote uses the same BS 8500 mix specification, sub-base depth, DPM, and reinforcement — comparing quotes on different specifications is misleading.
Concrete Slab — Frequently Asked Questions
Common questions about specifying, calculating, and constructing concrete slabs in the UK.
Minimum slab thickness in the UK depends on its purpose and loading:
- Patio / pedestrian path: 75–100mm minimum — 100mm recommended
- Domestic ground floor slab: 100mm minimum per NHBC Standards — 150mm recommended with A252 mesh reinforcement for all new build
- Domestic garage floor: 100mm minimum — 150mm recommended
- Concrete driveway (private cars): 100mm minimum — 150mm strongly recommended
- Driveway for vans / commercial vehicles: 150mm minimum — 175mm recommended
- Commercial / industrial floor slab: 150mm minimum — 200–250mm typically required
NHBC Standards Chapter 4.2 requires a minimum 100mm slab for new domestic construction but recommends 150mm as best practice. The Building Regulations Approved Document A does not specify slab thickness directly — it refers to BS 8004 for foundations and structural design standards for floor slabs.
Calculate concrete volume using the formula: Length (m) × Width (m) × Thickness (m) = Volume (m³). For example, a 8m × 5m slab at 150mm (0.15m) thick = 8 × 5 × 0.15 = 6.0 m³ net volume. Then:
- Add 10% waste: 6.0 × 1.10 = 6.6 m³
- Add pump prime if pumping: + 0.25 m³ = 6.85 m³
- Round up to nearest 0.5 m³: order 7.0 m³
- One standard 6 m³ ready-mix truck + 1.0 m³ second truck — or order 7.0 m³ as a slightly overfilled single truck load
Use the calculator at the top of this page to do this automatically including sub-base, mesh, and cost calculations in one step.
For a domestic concrete driveway in the UK, specify PAV1 (C30/37) to BS 8500 as the minimum. If the driveway is near roads treated with de-icing salt, or in a frost-affected location, specify PAV2 (C35/45) which has a lower W/C ratio and higher sulfate resistance. Key driveway concrete requirements:
- Mix: PAV1 (standard) or PAV2 (de-iced / frost-exposed)
- Strength: C30/37 minimum
- Maximum W/C ratio: 0.55 (PAV1) or 0.45 (PAV2)
- Minimum thickness: 100mm — 150mm strongly recommended for cars
- Reinforcement: A252 fabric mesh — reduces shrinkage cracking
- Sub-base: 200mm compacted MOT Type 1 minimum
- Surface finish: Brushed (anti-slip) — not power-floated or steel-trowelled (too smooth, slippery when wet)
Do not specify a standard RC mix for a driveway — PAV mixes are specifically designed for the freeze-thaw cycling and surface abrasion experienced by paved areas.
Planning permission requirements for concrete slabs depend on the location and use:
- Internal ground floor slab (new build): No separate planning required — covered under the main building consent. Building Regulations Approved Documents apply.
- Domestic driveway over 5m²: Permitted Development if using a permeable surface or drainage directing to a lawn/border. An impermeable concrete driveway over 5m² in a front garden requires planning permission per the 2008 householder permitted development changes.
- Patio / garden slab at rear: Generally permitted development — no planning consent needed for a domestic rear patio at ground level.
- Commercial / industrial floor slab: Planning permission and Building Regulations consent both required as part of the wider building works.
- Listed buildings or Conservation Areas: Always check with the local planning authority — restrictions apply even for ground works.
Building Regulations always apply to structural floor slabs, foundation slabs, and any slab forming part of a habitable building — regardless of planning status. Consult your local authority Building Control before commencing work.
Concrete slab cracking in the UK is almost always caused by one or more of these preventable factors:
- Shrinkage cracking: All concrete shrinks as it cures. Control joints (saw-cut or formed) at maximum 3–4m centres channel cracking to predictable locations. Without joints, cracks appear randomly.
- Insufficient reinforcement: Mesh reinforcement does not prevent cracking but holds cracks tight (hairline width) so they do not widen or become structural failures. Unreinforced slabs crack more visibly.
- Water added on site: Any site water addition increases the W/C ratio, reduces strength, and dramatically increases shrinkage. Never add water to ready-mix concrete.
- Inadequate sub-base: Soft spots in the sub-base cause differential settlement — the slab cracks where the bearing changes. Always compact sub-base with a vibrating plate compactor in maximum 150mm lifts.
- Poor curing: Concrete dried out too fast in sun or wind loses water before hydration completes — resulting in a weak, dusty surface and extensive cracking. Cure for minimum 7 days.
- Wrong mix / too thin: Using GEN3 instead of RC30/C, or laying 75mm where 150mm is required.
Concrete does not simply "dry" — it cures through a chemical hydration process that requires moisture and temperature above 5°C. Key UK curing milestones for RC30/C are:
- Initial set: 1–2 hours after placing (depending on temperature and admixtures)
- Foot traffic: 24–48 hours (carefully, no loaded vehicles)
- Light vehicle traffic (cars): 7 days minimum — never before
- Full design strength (28-day cube strength): 28 days
- Floor finishes / screed: Do not lay flooring until relative humidity of slab drops below 75% — typically 6–12 weeks depending on slab thickness and ambient conditions
In cold UK weather (below 10°C), curing is significantly slower — at 5°C, a concrete slab may take 3–4 times longer to reach equivalent strength compared to 20°C. Use insulating blankets and specify winter-grade concrete (accelerated admixture or hot mix) when pouring between November and March.