How do I calculate concrete volume?

Length × width × depth in metres gives cubic metres; multiply by 1,000 for litres. A 20kg bag of ready-mix yields about 10 litres.

Bagged or ready-mix delivery?

Bagged is fine up to about 0.25m³ (roughly 25 bags). Above that, a volumetric or ready-mix delivery is cheaper and far less work.

5–10 minutes to initial set — pour the dry mix into the wetted hole and it does the rest. Full strength takes about 24 hours.

Calculate how much concrete you need for post holes, shed bases and small slabs — from bags of post mix and ready-mix to larger volumetric jobs.

Enter the area and depth for slabs, or count your post holes. Post mix sets in 5–10 minutes with no mixing — one bag per standard fence post hole.

Start here

01 — The Calculator

Pick a material, pace out your plot, and the value engine prices every way to fill it — hippo bags, dumpy bags or handy sacks.

Plot shape

Length (m)

Width (m)

How deep?

10 cm

0102030 cm

Depth changes the volume a lot — 5cm mulch is normal, raised veg beds want 20cm+.

Volume

0 litres

Cubic

0.00 m³

Area

0.0 m²

Est. weight

0.00 tonnes

Enter your plot dimensions and the value engine will price the cheapest way to cover it.

Worked example: fencing a 20m run

12 posts (11 bays plus ends) needs 12 bags of post mix. A small 2m² shed base at 10cm deep is 200 litres — about 10–12 bags of ready-mix concrete.

One 20kg bag per standard hole (about 200×200×600mm). Use two bags for gate posts or exposed, windy sites.