Concrete Calculator

Work out the concrete volume for a slab, footing or post hole, in cubic metres, yards and bags.

Concrete calculator

What are you pouring?

Length (m) Width (m)

Depth or thickness (m)

Post hole diameter (m) Number of holes

Bag size

Volume: — · Cubic yards: —

Cubic feet: — · Litres: —

Bags of mix: —

—

Ready mix is sold by the cubic metre, so order a little more than the calculated volume for spillage.

Common questions about the free online concrete calculator.

For a slab or footing multiply length by width by depth. For a round post hole use the diameter, the depth and the number of holes.

A 20 kilogram bag yields about 0.009 cubic metres, so a cubic metre takes roughly 110 bags, and 25 kilogram bags take about 89.

Add 5 to 10 percent for spillage and uneven ground, because running short mid pour is expensive and can weaken the job.

A garden path or shed base is usually 75 to 100 millimetres, while a driveway or garage base needs 100 to 150 millimetres.

A common rule is one third of the post length below ground, so a 2.4 metre post needs about 800 millimetres in the ground.

Multiply cubic metres by 1.308, so 1.2 cubic metres is about 1.57 cubic yards, which is how ready mix is often sold.

Cement is one ingredient of concrete. A concrete mix blends cement with sand, stone and water to make the finished material.

Light foot traffic is usually fine after 24 to 48 hours, but full strength takes about 28 days of curing in damp conditions.

No. The volume and bag estimate runs in your browser and nothing you enter is sent to a server.

Yes. It is completely free, needs no account and you can estimate as many pours as you like.

Last updated: October 10, 2026