The path along the side of our house was one of the first concrete jobs I did myself. It was about 12 metres long and 1 metre wide, running from the front garden round to the back gate. I had looked up the calculation, worked out I needed just under 1.2 m3 at 100mm depth, and hired a small electric mixer for the day.
What I had not calculated was how many bags of 25kg concrete mix that actually translated to - about 100 bags. And I had not appreciated how heavy 100 bags of concrete mix is, or how long it would take to mix them all, or how hard the path would be to level and finish while working alone.
I got it done, but it took a very long day and every muscle in my back knew about it the following week. For anything over about 0.5 m3 I would now go straight to a hired transit mixer or ready-mix without hesitation.
The formula
Volume (m3) = Length (m) x Width (m) x Thickness (m)
If thickness is in mm, divide by 1000.
For a 12m x 1m path at 100mm thick:
- Volume = 12 x 1 x 0.1 = 1.2 m3
- Add 10% wastage = 1.32 m3
- Ready-mix: round up to 1.5 m3 (typical supplier minimum increment)
For an accurate figure for your exact dimensions, use the Concrete Base Calculator.
How thick does a path need to be?
| Path type | Recommended thickness |
|---|---|
| Light garden path, foot traffic only | 75mm |
| Standard path alongside house | 100mm |
| Side access path, possible vehicle use | 100-125mm |
| Path to garage entrance | 100-125mm |
| Heavily trafficked path | 125mm |
75mm is acceptable for a purely decorative garden path where no vehicle will ever go. 100mm is the more practical standard that gives more margin for error and handles the occasional barrow or bike. Going below 75mm on anything that will take regular use is false economy.
Bags vs ready-mix: the honest breakdown
| Volume | 25kg bags needed | My recommendation |
|---|---|---|
| Under 0.3 m3 | Under 25 bags | Bags, no mixer needed |
| 0.3-0.5 m3 | 25-42 bags | Bags with a hired mixer |
| 0.5-1.0 m3 | 42-84 bags | Mixer hire strongly recommended |
| 1.0-2.0 m3 | 84-167 bags | Ready-mix or large mixer hire |
| Over 2.0 m3 | 167+ bags | Ready-mix, no question |
The numbers really put it in perspective. 84 bags is roughly 2.1 tonnes of dry material - that is a lot of lifting, opening, tipping and mixing before you have even started pouring. A small ready-mix order at these volumes is usually cheaper per m3 and far less physically demanding.
Concrete quantities for common path sizes
At 100mm depth with 10% wastage:
| Path dimensions | Area | 25kg bags | Ready-mix |
|---|---|---|---|
| 3m x 0.9m | 2.7m2 | 25 bags | 0.25 m3 |
| 5m x 0.9m | 4.5m2 | 41 bags | 0.5 m3 |
| 5m x 1.0m | 5.0m2 | 46 bags | 0.5 m3 |
| 8m x 1.0m | 8.0m2 | 73 bags | 1.0 m3 |
| 10m x 1.0m | 10.0m2 | 92 bags | 1.25 m3 |
| 10m x 1.2m | 12.0m2 | 110 bags | 1.5 m3 |
| 15m x 1.0m | 15.0m2 | 138 bags | 1.75 m3 |
| 15m x 1.2m | 18.0m2 | 165 bags | 2.0 m3 |
At 0.012 m3 yield per 25kg bag. Ready-mix rounded to nearest 0.25 m3.
Should I use a sub-base?
Yes, in most cases. A 75mm compacted sub-base of MOT Type 1 or well-compacted hardcore improves drainage, provides a stable base and extends the life of the concrete.
The main exception where you might skip it:
- A very short decorative path (under 3m)
- Well-drained sandy or gravelly soil
- Sheltered position, no risk of heavy loading
If there is any possibility of the path being used by wheeled loads (barrows, bikes, mobility scooters) or if the soil is clay, include the sub-base. It costs relatively little in material and makes a meaningful difference.
Use the Sub Base Calculator to work out the sub-base quantities alongside the concrete.
How to set up formwork
Before any concrete goes in, the formwork needs to be right. For a path, this is usually timber boards held in position by stakes:
- Boards: 25mm x 100mm treated timber for a 100mm deep path
- Stakes: 50mm x 50mm timber at roughly 1m intervals outside the boards
- Setting out: Use a string line and spirit level to get boards level and at the correct height
Set the falls (drainage slope) at formwork stage. A path running alongside a building should slope very gently away from the house - aim for about 1:60 (roughly 16mm per metre). This is barely visible to the eye but keeps water draining away from the building.
What concrete mix to use for a path
For a garden path, C20 (GEN3/ST2) is fine if cost is a factor. C25 (GEN4/ST4) is better and worth the small extra cost for a path that will see regular use - it has better abrasion resistance and durability.
For ready-mix, ask for C20 or C25. For bags, the standard "general-purpose concrete mix" or "all-in one" concrete bags are appropriate.
My tips for laying a concrete path
After that very long first day and several paths since:
Work in sections if using bags. Divide a longer path into manageable bays using thin plywood or hardboard dividers. This lets you complete one section properly before moving to the next, and the section boundaries become your expansion joints. Mix one section at a time rather than trying to mix all the concrete before pouring any of it.
Overfill slightly then screed back. Pour the concrete slightly higher than the formwork boards, then use a straightedge board to screed it back level. Pulling excess concrete forward and working it level in one pass is much easier than trying to fill low spots after the fact.
Finish with a wood float, not a steel float. A wood float leaves a slightly textured surface which is safer underfoot when wet. A steel float creates a very smooth, slippery finish that looks nice but is a hazard in winter.
Form the joins neatly. At the end of a working session, cut the edge of the new concrete straight with a trowel rather than leaving it rough. A clean butt joint to the next section is almost invisible once set.
Keep it damp while it cures. In dry or windy weather, lay polythene sheeting or damp hessian over the path for 3-7 days after pouring. Concrete that dries too fast develops a weak, dusty surface layer.
Use the Concrete Base Calculator to get accurate bag counts and ready-mix volumes before you start.