A concrete driveway is one of the best investments you can make in a house. Once done properly it is genuinely low maintenance, handles any vehicle you might own, and will last 30-50 years with minimal attention. The key word is properly.
A neighbour poured his own driveway a few years back. He calculated the concrete volume correctly, booked the ready-mix, and the pour went well. The problem emerged the following winter. Cracks appeared, not catastrophic but visible, running across two sections of the slab. When we talked about it, he realised he had specified C20 concrete when C25 was the minimum, and his sub-base had been only 75mm of badly compacted hardcore. Two spec failures, not one.
The slab is still there, still functional, but it looks like what it is - a job that was close but not quite right. This guide is about getting both right.
Why ready-mix is the only realistic option
For a driveway of any meaningful size, the maths makes bags impractical very quickly.
At 100mm depth, a 20m2 driveway needs 2.0 m3 of concrete plus wastage - roughly 185 bags of 25kg concrete mix. At 150mm, it is 275 bags. Nobody sensibly mixes 275 bags of concrete by hand, or even with a hired mixer. Ready-mix is both cheaper per m3 at this volume and the only way to achieve a consistent, pourable slab in a single session.
The formula
Volume (m3) = Length (m) x Width (m) x Thickness (m)
Always add at least 10% wastage and round up to the nearest 0.25 m3 (typical ready-mix minimum increment).
Worked examples
Single car driveway: 5m x 5m, 150mm thick
- Volume = 5 x 5 x 0.15 = 3.75 m3
- Add 10% = 4.125 m3
- Order: 4.25 m3
Double driveway: 8m x 5m, 150mm thick
- Volume = 8 x 5 x 0.15 = 6.0 m3
- Add 10% = 6.6 m3
- Order: 6.75 m3
For your exact dimensions, use the Concrete Base Calculator.
Volume by common driveway size
At 150mm depth, 10% wastage, rounded to nearest 0.25 m3:
| Driveway dimensions | Area | Ready-mix to order |
|---|---|---|
| 4m x 3m | 12m2 | 2.25 m3 |
| 5m x 3m | 15m2 | 2.75 m3 |
| 5m x 4m | 20m2 | 3.5 m3 |
| 5m x 5m | 25m2 | 4.5 m3 |
| 6m x 4m | 24m2 | 4.25 m3 |
| 8m x 4m | 32m2 | 5.5 m3 |
| 8m x 5m | 40m2 | 7.0 m3 |
| 10m x 5m | 50m2 | 8.75 m3 |
How thick?
| Situation | Minimum | Recommended |
|---|---|---|
| Cars only, good ground | 100mm | 125-150mm |
| Standard residential | 100mm | 150mm |
| SUVs or occasional vans | 125mm | 150mm |
| Regular van or commercial use | 150mm | 175mm |
150mm is the right target for most residential driveways. It handles ordinary vehicle loads, tolerates minor sub-base variation, and is the figure most driveway contractors in the UK use as their standard.
Sub-base: not optional
Before the concrete, you need a proper sub-base. This is not an optional extra - it is what determines whether your driveway cracks in two years or lasts thirty.
For a concrete driveway:
- Excavate to 280-320mm below finished level
- Lay geotextile membrane
- Compact 100-150mm of MOT Type 1 sub-base
- Lay DPM (1000 gauge polythene)
- Pour and finish the concrete slab
Use the MOT Type 1 Calculator to work out sub-base quantities. For a 20m2 driveway with 150mm compacted sub-base, expect to need roughly 10-12 tonnes of MOT Type 1.
What concrete to specify
C25 minimum. This is the minimum grade recommended for a residential driveway in the UK. Ask for C25 (GEN4/ST4), slump class S2 or S3.
C30 is better for exposed driveways where abrasion and freeze-thaw resistance are important. The cost difference is typically small per m3.
Do not accept C15 or C20 for a driveway surface. Some unscrupulous contractors sub-spec the concrete to save money - knowing what grade to ask for protects you.
Expansion joints
Concrete shrinks slightly as it cures and expands in warm weather. Without expansion joints, it will crack where it pleases. With planned joints, cracks happen at the joints where you can deal with them neatly.
For a driveway:
- Form or saw-cut joints at 3-4m intervals
- Include a joint around any fixed features (drain covers, inspection chambers, piers)
- Joint depth should be at least 25-30% of slab thickness
Softboard joint formers or proprietary plastic joint profiles both work well. Do not try to do without joints on any slab over about 10-12m2.
My tips for a successful concrete driveway pour
Plan the access for the ready-mix truck before you book it. A standard ready-mix drum truck is about 2.4m wide and needs clearance for the chute (up to 5m reach). If the truck cannot get close, ask about a pump - it costs more but can reach over obstacles. Be upfront about access when you call for a quote.
Have at least two people for the pour. One directs the chute and keeps the concrete moving, the other spreads and screeds. Trying to do a driveway pour alone is genuinely very difficult and the concrete starts to stiffen before you finish.
Work quickly but do not rush. Ready-mix has a working life of about 1.5-2 hours from batching (longer in cold weather, shorter in hot sun). You have time to do the job well, but do not take long breaks.
Do not add water on site. If the concrete seems too stiff, resist the urge to add water from a hose. Too much water weakens the mix significantly. If the mix is genuinely too stiff, call the supplier - they may be able to send a plasticiser.
Cure for at least 3-7 days. Cover with polythene sheeting held down at the edges to keep moisture in during curing. In hot or windy weather this is critical - concrete that dries too quickly on the surface develops a weak, dusty layer.
Get your volume confirmed with the Concrete Base Calculator before calling the ready-mix supplier.