Concrete Volume Calculator — How Much Concrete Do I Need?

A typical 3m x 2.4m shed base at 100mm thick needs approximately 0.72 m3 of concrete. With 10% wastage, order 0.8 m3. For small jobs like this, bagged premix (around 88 x 20kg bags at 0.009 m3 each) is often more practical than ordering a ready-mix lorry. Use our Concrete Mix Calculator to work out the cement, sand and aggregate needed if mixing on site.

As an indicative 2026 guide, standard domestic ready-mix (around C25/30) typically runs £90-£130 per m³ before VAT — so roughly £540-£780 for a 6m³ load. Cheaper non-structural grades (blinding, C15/20) start nearer £80/m³, while higher-strength mixes and London/South East prices can reach about £150/m³. Most suppliers also apply a short-load surcharge of roughly £50-£150 on small pours (under about 4-6m³), so ready-mix is most cost-effective for jobs of 1m³ or more. Figures vary by grade, region and order size — confirm with your local supplier.

Each standard 20kg bag of premix concrete makes roughly 0.009 m³ of mixed concrete (about 9 litres), so you need around 111-112 × 20kg bags to make 1m³. This calculator always rounds up to whole bags, so it shows 112 for a 1m³ pour. For anything above about 0.5 m³ it is usually cheaper and easier to order ready-mix.

Yes, always add 10% wastage for concrete work. Concrete is lost through spillage, uneven ground, over-excavation, and settling. For trenches in rough ground you may need 15-20% extra. Running short on a pour is a serious problem, so it is always better to over-order slightly.

For a standard domestic shed base or patio slab, 100mm (4 inches) is typical. A garage base needs 150mm minimum, ideally with mesh reinforcement. Foundations for walls must meet Building Regulations Approved Document A — typically 225mm minimum depth concrete in the trench. Use our Foundation Calculator for trench and foundation concrete volumes, or our Rebar Calculator if your slab needs reinforcement.