Concrete calculator
Work out how much concrete you need for a slab, base or footing. Enter the length, width and depth and this calculator gives you the volume in cubic metres, the ready-mix order, and the cement and ballast if you are mixing your own.
Concrete calculator
Enter your measurements in metres. Everything updates as you type, and nothing is sent anywhere.
Figures include a 10% allowance for waste and spillage. Mix-your-own quantities assume a general-purpose 1:5 all-in ballast mix, roughly 12 bags of 25kg cement and 1.8 tonnes of ballast per cubic metre. Structural work such as foundations needs a stronger mix, so confirm quantities with your merchant.
Common questions
How much concrete do I need?
Multiply the length by the width by the depth to get the volume in cubic metres. A 4m by 3m slab at 100mm deep is 1.2 cubic metres, for example. Add about 10% for waste and uneven ground, which this calculator does for you.
How many bags of cement per cubic metre of concrete?
For a general 1:5 all-in ballast mix, roughly 12 bags of 25kg cement and about 1.8 tonnes of ballast make one cubic metre of concrete. A stronger mix for foundations or structural work uses more cement, so check the spec before you order.
Is ready-mix or mixing your own cheaper?
Mixing your own is cheaper on materials for small jobs, but ready-mix saves a lot of hard work and gives a more consistent result. Once you are past about half a cubic metre, most people find ready-mix or a mix-on-site lorry better value than bagging it by hand.
What depth of concrete do I need?
Around 100mm for a shed base or path, 100mm to 150mm for a driveway, and thicker with steel reinforcement for anything carrying heavy loads. Always lay concrete on a compacted sub-base.
These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing. These quantities are a guide to help you order. Always round up and check with your supplier before buying.