Concrete Calculator - Volume & Cost Estimator
Calculate the exact amount of concrete needed for your UK construction project. Our free calculator works out the volume in cubic metres, number of bags required, weight in tonnes, and estimated cost. Whether you're laying a patio, building a driveway, pouring a shed base, or constructing foundations, get accurate measurements to avoid ordering too much or too little.
Quick Reference: UK Concrete Volumes
Calculate Concrete Required
How to Calculate Concrete Volume
Calculating the volume of concrete needed is straightforward using basic geometry. The key is to ensure all measurements are in the same units before calculating.
The Basic Formula
Volume (m³) = Length (m) × Width (m) × Depth (m)
Circular Slab:
Volume (m³) = π × Radius² × Depth = π × (Diameter/2)² × Depth
Remember: Convert cm to metres by dividing by 100
Worked Example: Patio Slab
Project: Garden patio measuring 4m × 3m with 100mm (10cm) depth
- Convert depth: 10cm ÷ 100 = 0.1m
- Calculate volume: 4m × 3m × 0.1m = 1.2 m³
- Add 10% wastage: 1.2 × 1.10 = 1.32 m³
- Weight: 1.32 × 2.4 = 3.17 tonnes
- Order: 1.5 m³ (round up to nearest 0.5)
Why Add Wastage?
Always add 5-15% extra for wastage, spillage, uneven ground, and compaction losses. For complex shapes or inexperienced pourers, add 15%. Ready-mix suppliers typically have minimum orders, so rounding up slightly often makes sense anyway.
UK Concrete Grades Explained
In the UK, concrete is classified by its compressive strength at 28 days, measured in Newtons per square millimetre (N/mm²). The "C" number indicates this strength rating.
C15
15 N/mm²
Blinding, levelling, fill
Non-structural only
C20
20 N/mm²
Domestic floors, light use paths
Internal applications
C25
25 N/mm²
Patios, shed bases, paths
Most domestic external use
C30
30 N/mm²
Driveways, garage floors
Vehicle traffic areas
C35
35 N/mm²
Commercial foundations
Heavy-duty applications
C40+
40+ N/mm²
Industrial, structural
Specialist applications
Which Grade for Your Project?
| Application | Minimum Grade | Recommended Depth | Reinforcement |
|---|---|---|---|
| Garden path (foot traffic only) | C20 | 75-100mm | Optional mesh |
| Patio slab | C25 | 100mm | A142 mesh |
| Shed/summerhouse base | C25 | 100mm | Optional mesh |
| Driveway (cars only) | C30 | 100-150mm | A193 mesh |
| Driveway (vans/caravans) | C30 | 150mm | A252 mesh |
| Garage floor | C30 | 100-125mm | A193 mesh |
| Foundation footings | C25-C35 | As per plans | Per Building Regs |
| Extension base slab | C30-C35 | Per structural engineer | Per Building Regs |
Building Regulations
For structural work (foundations, extensions, load-bearing elements), concrete specification must comply with UK Building Regulations. You'll typically need a structural engineer's specification and Building Control approval. Ready-mix concrete suppliers provide documentation of concrete grade and slump for compliance records.
Recommended Concrete Depths for Common Projects
Getting the depth right is crucial. Too thin and the concrete will crack under load; too thick wastes money and materials.
| Project Type | Minimum Depth | Recommended | Sub-base Required |
|---|---|---|---|
| Garden stepping stones | 50mm | 75mm | Optional (50mm) |
| Path (foot traffic) | 75mm | 100mm | 75-100mm MOT Type 1 |
| Patio | 100mm | 100mm | 100mm MOT Type 1 |
| Shed base (small) | 75mm | 100mm | 75mm MOT Type 1 |
| Shed base (large/heavy) | 100mm | 125mm | 100mm MOT Type 1 |
| Hot tub base | 125mm | 150mm | 150mm MOT Type 1 |
| Domestic driveway (cars) | 100mm | 125-150mm | 150mm MOT Type 1 |
| Driveway (heavy vehicles) | 150mm | 200mm | 200mm MOT Type 1 |
| Garage floor | 100mm | 125mm | 150mm MOT Type 1 |
Sub-base is Essential
Never pour concrete directly onto soil. Always prepare a compacted sub-base of MOT Type 1 (crushed stone) or hardcore. This provides drainage, prevents frost heave, and ensures even support. Compact using a whacker plate or hand tamper. For domestic driveways, 100-150mm compacted sub-base is typically sufficient.
UK Concrete Costs Guide (2024/2025)
Concrete costs vary by type, quantity, location, and supplier. Here's a general guide to help you budget:
Ready-Mix Concrete (Delivered by Truck)
Standard Mix (C25)
£65-£85 per m³
Most common for domestic use
High Strength (C30-C35)
£75-£95 per m³
Driveways, structural work
Delivery Charge
£100-£200
Varies by location/supplier
Minimum Order
3-6 m³ typical
Under-load charges may apply
Bagged Concrete (From DIY Stores)
| Product | Price per Bag | Coverage per Bag | Cost per m³ |
|---|---|---|---|
| Postcrete (25kg) | £4-£6 | ~0.011 m³ | ~£450-£550 |
| Ready Mix Concrete (25kg) | £5-£7 | ~0.0125 m³ | ~£400-£560 |
| Ballast (25kg) + Cement | £3-£4 | Varies by mix | ~£150-£250 |
| Bulk bag ballast (850kg) | £50-£70 | ~0.5 m³ | ~£100-£140 |
Cost Comparison: 2m³ Driveway Slab
| Ready-Mix: | 2m³ × £80 + £150 delivery = £310 |
| Bagged (25kg): | 160 bags × £5 = £800 |
| Mix Your Own: | Cement + Bulk Ballast = £200-£350 |
For quantities over 0.5m³, ready-mix is usually more economical and significantly faster.
UK Ready-Mix Suppliers
Major UK suppliers include Hanson, Cemex, Aggregate Industries, Tarmac, and many local independents. Volumetric (mix-on-site) suppliers like Mix On Site are ideal for medium quantities (0.5-3m³) as you only pay for what you use. Always get quotes from 2-3 suppliers.
Mixing Concrete Yourself
For small projects (under 0.5m³), mixing your own concrete can be economical. Here are the standard UK mixing ratios:
Standard Mix Ratios (by Volume)
| Grade | Cement | Sharp Sand | Gravel (10-20mm) | Use |
|---|---|---|---|---|
| C15-C20 | 1 part | 2 parts | 4 parts | Paths, light use |
| C25 | 1 part | 1.5 parts | 3 parts | Patios, shed bases |
| C30 | 1 part | 1 part | 2 parts | Driveways, garages |
Materials Needed per Cubic Metre
| Mix Type | Cement (25kg bags) | Sharp Sand (bulk bags) | Gravel (bulk bags) |
|---|---|---|---|
| C20 (1:2:4) | 6-7 bags | 0.5 bags (~450kg) | 1 bag (~900kg) |
| C25 (1:1.5:3) | 8-9 bags | 0.5 bags (~450kg) | 0.75 bags (~700kg) |
| C30 (1:1:2) | 10-12 bags | 0.4 bags (~360kg) | 0.6 bags (~540kg) |
Mixing Tips
- Water: Add gradually until mix is workable but not sloppy. Too much water weakens concrete.
- Consistency: Should hold its shape when squeezed, not crumble or slump flat.
- Mixing time: Mix for at least 3-5 minutes until uniform colour.
- Working time: Use within 45-60 minutes of mixing before it starts to set.
Safety Warning
Wet concrete is highly alkaline and can cause serious chemical burns. Always wear waterproof gloves, safety glasses, and long sleeves. If concrete contacts skin, wash immediately with clean water. Seek medical attention for any burns or if concrete gets in eyes.
Weather Considerations for UK Conditions
UK weather can significantly affect concrete work. Plan your pour carefully.
Temperature Guidelines
| Condition | Temperature | Action |
|---|---|---|
| Ideal | 10-25°C | Normal pouring, standard curing |
| Cool | 5-10°C | Slower curing, may need longer before loading |
| Cold | 0-5°C | Use frost protection or rapid-set additives |
| Freezing | Below 0°C | DO NOT POUR - concrete will be damaged |
| Hot | Above 25°C | Pour early morning, use retarder, mist cure |
UK Seasonal Advice
- Spring (Mar-May): Ideal season. Check forecast for late frosts.
- Summer (Jun-Aug): Good but cure carefully in hot spells. Start early morning.
- Autumn (Sep-Nov): Good early season. Avoid late pours - check frost forecasts.
- Winter (Dec-Feb): Generally avoid unless using rapid-set/heated enclosures.
Rain Protection
Before pouring: Don't pour if heavy rain is forecast within 2-4 hours.
During pouring: Light drizzle is usually OK. Heavy rain can wash cement from surface.
After pouring: Cover with polythene if rain expected in first 24 hours.
Curing: Keep concrete damp for 7 days in hot/dry weather to prevent cracking.
Planning Permission and Building Regulations
Driveways and Hard Surfaces
Since 2008, new or replacement driveways in England using impermeable materials (standard concrete, tarmac) larger than 5 square metres require planning permission UNLESS:
- Water drains onto a lawn, border, or soft landscaping area
- You use permeable paving materials
- Water drains to a soakaway or sustainable drainage system (SuDS)
Permitted Development Rights
Patios, paths, and hard surfaces not at the front of the property are generally permitted development (no permission needed) unless your home is listed or in a conservation area. For driveways, check with your local planning authority before starting work.
Building Regulations
Building Regulations approval is required for:
- Foundation work for extensions or new buildings
- Structural concrete (load-bearing elements)
- Garage slabs attached to a dwelling
- Any work requiring structural calculations
Building Regulations are NOT typically required for:
- Patios and paths
- Driveways
- Detached shed/outbuilding bases (under certain size limits)
Frequently Asked Questions
A typical UK single-car driveway (3m × 6m) needs 1.8 cubic metres at 100mm depth, or 2.7m³ at 150mm depth. Add 10% for wastage. For cars only, use 100mm minimum; for heavier vehicles, 150mm. Use C30 grade concrete and always include steel mesh reinforcement.
C25 is suitable for most domestic external use (patios, shed bases, paths). C30 is recommended for driveways and garage floors that take vehicle loads. C35+ is for commercial and heavy-duty structural applications. Always check Building Regulations requirements for structural work.
A 25kg bag of ready-mix concrete yields approximately 0.0125 cubic metres. Therefore, you need about 80 bags per cubic metre. For larger projects, ready-mix concrete is far more practical and economical than bags.
75mm for garden paths, 100mm for patios and shed bases, 100-125mm for domestic garages, 100-150mm for car driveways, 150-200mm for heavy vehicle driveways. Always pour onto a compacted MOT Type 1 sub-base.
Ready-mix typically costs £65-£85 per cubic metre for standard grades (2024/2025 prices), plus delivery of £100-£200. Minimum order is usually 3-6m³. For small quantities, bagged concrete costs around £400-£500 per cubic metre but is much more labour-intensive.
You can walk carefully on concrete after 24-48 hours. Light foot traffic is safe after 48-72 hours. Wait 7 days before driving on it, and 28 days for full strength. In cold weather, double these times. Keep the surface moist for 7 days for proper curing.
If your impermeable driveway exceeds 5 square metres and doesn't drain to a lawn or soakaway, you need planning permission. Permeable concrete or proper drainage can avoid this requirement. Check with your local council before starting work.
Yes, steel mesh reinforcement (A142 or A193) is recommended for all external concrete slabs over 75mm thick. It prevents cracking and improves load-bearing capacity. Place mesh on spacers at mid-depth of the slab. Essential for driveways.
Pro Tips for Accurate Results
- Double-check your input values before calculating
- Use the correct unit format (metric or imperial)
- For complex calculations, break them into smaller steps
- Bookmark this page for quick future access
Understanding Your Results
Our Concrete Calculator provides:
- Instant calculations - Results appear immediately
- Accurate formulas - Based on official UK standards
- Clear explanations - Understand how results are derived
- 2025/26 updated - Using current rates and regulations
Common Questions
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