How thick should a concrete path be?

A hundred millimetres, or four inches, is the general answer for a domestic path and it covers most situations. You can drop to seventy-five for a purely decorative garden path that will never see anything heavier than a person, though it leaves little margin. Anything a vehicle might cross — even occasionally, even just a wheelbarrow route that a car sometimes uses — wants a hundred and twenty-five, and a genuine driveway wants a hundred and fifty on a deeper sub-base.

How far apart should control joints be on a path?

Take the smaller of two figures: twenty-four times the slab thickness, and one and a half times the path width. On a path the width rule almost always wins, because paths are narrow. A 1.2 metre path at 100 mm thick gives 2.4 m from the thickness rule but only 1.8 m from the shape rule, so 1.8 m is the answer. The point of the shape rule is that a long thin panel behaves like a beam and cracks across its middle; keeping panels near square gives the shrinkage nowhere obvious to go.

When and how deep do I cut the joints?

Within twenty-four hours of pouring, and a quarter of the slab depth. On a 100 mm slab that is 25 mm. Cut too shallow and the slab cracks somewhere else instead, ignoring your joint entirely; cut too late and it will already have cracked where it wanted to. You can either tool them in while the concrete is still plastic using a groover, which is easiest on a small path, or saw-cut them once it has hardened enough not to ravel at the edges but before it has been through a full night of cooling.

Do I need a sub-base under a path?

For anything you want to last, yes. A hundred millimetres of compacted crushed stone under a path spreads the load, gives you a level surface to work from, and — most importantly — drains. Concrete sitting directly on clay soil moves with every wet and dry cycle and every frost, and there is nothing the slab can do about it. The exception is genuinely firm, free-draining ground such as compacted gravel or sound rock, where the ground already does the sub-base job.

Why does sub-base need a compaction allowance?

Because it is specified as a finished depth but sold as a loose volume, and the two differ by roughly a quarter. Crushed stone delivered loose contains a great deal of air between the particles, and compacting it drives that out. If you order the finished depth you will end up around 20% short and the path will sit low, which on a path against a house wall or a step is a genuine problem rather than a cosmetic one. The calculator adds the allowance automatically and shows both figures.

Yes, across its width rather than along its length, and only slightly — about one in eighty, which is roughly 15 mm across a 1.2 metre path. That is enough for water to run off without being noticeable underfoot. A dead level path holds puddles, and a puddle that freezes is both a hazard and a way of working water into the surface where it spalls the concrete over successive winters. Always fall away from a building, never towards one.

Does a path need reinforcement?

A domestic path on a properly compacted sub-base with sensible joint spacing generally does not, and mesh is often added out of habit rather than need. Where it earns its place is over ground that may move — made-up ground, recent excavation, near trees — or where the path crosses a service trench, or where vehicles will use it. Fibre reinforcement mixed into the concrete is a reasonable middle option for crack control, though it does not replace steel where there is actual structural demand.

What edging does a path need?

Something to hold the edges, either the formwork removed after the pour or a permanent restraint left in place. Concrete edges are the vulnerable part of a path: they have no lateral support, they take the impact of mower wheels and foot traffic stepping off, and they are where frost damage starts. Timber forms are fine for the pour and can be removed once the concrete has gained strength, but on a path bordered by soft ground a permanent edging of brick, block or treated timber will meaningfully extend its life.

How do I finish the surface?

Broom it across the direction of travel once the surface water has gone but while the concrete is still workable. A smooth steel-trowelled finish looks appealing indoors and is dangerously slick outdoors as soon as it rains, which for a path is exactly the wrong tradeoff. Draw the broom perpendicular to the way people walk so the texture grips the sole. Then keep the slab damp for several days: fast drying is the single most common cause of surface crazing, and it is entirely preventable.

Concrete Path Calculator

A concrete path is the simplest slab there is to calculate and one of the easiest to get wrong in ways that only show up a year later. The volume itself is length times width times thickness, and if that were the whole job this page would not need to exist. What separates a path that lasts from one ...

THE PATH

SECTIONS — LEAVE LENGTH AT 0 IF UNUSED

SECTION 1 LENGTH (m)

WIDTH (m)

SECTION 2 LENGTH (m)

WIDTH (m)

SECTION 3 LENGTH (m)

WIDTH (m)

SLAB THICKNESS (mm)

SUB-BASE DEPTH (mm) — 0 IF NONE

CONCRETE REQUIRED

1.58 m³

14.40 m² at 100 mm · including 10% waste · 3.80 tonnes

SUB-BASE

3.02 t

EDGING

24.0 m

JOINTS

Cut 6 joints, giving 7 panels. Spacing is set by panel shape rather than slab thickness, which is normal on a path — a panel much longer than one and a half times its width becomes a strip, and strips crack across their middle. That gives 1.8 m centres. Cut them within 24 hours of pouring, a quarter of the slab depth deep.

Total area

14.40 m²

Concrete before waste

1.440 m³

With 10% waste

1.584 m³

Weight

3.80 t

Sub-base compacted

1.440 m³

Sub-base to order

1.800 m³ loose

Sub-base weight

3.02 tonnes

Edging / formwork

24.0 m

Panels

7 at 1.71 m

Bags / loads

94 / 1

LAYING IT

Excavate to 200 mm below finished level and set 24.0 m of edge form, checking the fall as you go.

Lay and compact 1.800 m³ of sub-base in layers to a finished 100 mm. It arrives loose and settles about a quarter, so order the loose figure.

Place 1.584 m³ of concrete, working from one end and screeding off the forms. Lay a slight fall across the width so water runs off.

Cut 6 control joints within 24 hours, a quarter of the slab depth. Then keep it damp for several days — fast drying is what cracks a path.

THE PATH

Concrete cracks. The only question is where. It shrinks as it cures and keeps moving with temperature afterwards, and a path is a long thin shape with nowhere for that movement to go. A control joint is a deliberate line of weakness that decides the answer in advance, so the crack forms straight, below the surface, and stays closed. Here that means 6 joints at 1.8 m centres.

Sub-base is quoted as the finished compacted depth, but it is delivered loose and settles by about a quarter — so order 1.800 m³ to finish at 100 mm, roughly 3.02 tonnes.

Live calculation · updates as you type

Created with❤️byeaglecalculator.com

HOW TO USE

1
Enter the length and width of your path. If it changes width partway, or turns a corner into a different run, use the second and third section rows — leave their length at zero if you only have one straight run.
2
Set the slab thickness. Seventy-five millimetres is enough for foot traffic only, a hundred is the general answer, and anything a vehicle will cross wants a hundred and twenty-five or more.
3
Set the sub-base depth. A hundred millimetres of compacted granular material suits most paths; leave it at zero only if you are pouring onto genuinely firm, well-drained ground.
4
Read the concrete, the sub-base as a loose order quantity, the edging length, and the control joint count. The joint figure is the one worth acting on — cut them within a day of pouring, a quarter of the slab depth deep.

THE FORMULAS

AreaΣ length × width

Concretearea × thickness × (1 + waste)

Sub-base compactedarea × sub-base depth

Sub-base to ordercompacted × 1.25

Sub-base weightcompacted × 2.1 t/m³

Edging2 × length per section

Joint spacingmin(24 × thickness, 1.5 × width)

Panelsceil(length / spacing)

PATH THICKNESS AND JOINT SPACING

Use	Width	Thickness	Sub-base	Joints every
Garden path, foot traffic	0.9 m	75 mm	75 mm	1.35 m
General path	1.2 m	100 mm	100 mm	1.80 m
Wide path or side access	1.5 m	100 mm	100 mm	2.25 m
Occasional vehicle	2.4 m	125 mm	150 mm	3.00 m
Driveway grade	3.0 m	150 mm	200 mm	3.60 m

Notice that joint spacing tracks width rather than thickness in every row. Paths are narrow, so the rule that keeps panels near square binds before the one about slab depth does. On a wide slab it would be the other way round.

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Last updated: July 27, 2026 · Formula verified · Eagle-eyed accuracy for every calculation.