Calculator
Concrete calculator: cement and ballast
Concrete volume is length × width × depth; for a 1:5 mix allow about 15 bags of 25 kg cement and 2.2 tonnes of all-in ballast per cubic metre, plus a little extra for waste.
Enter your sizes, see the materials and a diagram, then send the list for a delivered price.
Quantities are estimates using standard UK rules of thumb and are shown with their working. We check them against your job before we price anything.
How the calculation works
- Volume = length × width × depth (in metres)
- Dry volume = volume × 1.54
- Cement = dry volume ÷ (1 + ballast parts), at 1,440 kg/m³
- Ballast = the rest, at about 1.7 tonnes per m³; + 5% waste
Worked example
A shed base 3 m × 2.4 m × 100 mm: 0.72 m³. At 1:5 with 5% extra, 12 bags of cement (rounded up) and about 1.65 tonnes of all-in ballast.
What to order with it
- Ballast & Gravel: All-in ballast, shingle, pea gravel and decorative stone.
- Cement: 25 kg bags of general-purpose and rapid-set cement.
- Bagged Concrete & Mortar Mixes: Post mix, ready-to-use concrete, mortar and screed in bags.
Quantities are estimates. Pack sizes, bag weights and coverage vary by manufacturer; we confirm them on your quote.
Questions
How much ballast for a cubic metre of concrete?
Roughly 2 to 2.2 tonnes of all-in ballast with about 15 bags of cement at a 1:5 mix. Our concrete calculator works out your slab or footing.
How many bags of cement for 1,000 bricks?
At a 1:4 mortar mix, about 8 to 9 bags of 25 kg cement and roughly 1 tonne of building sand, allowing for waste.
Send your list, get a delivered price
Tell us what you need and where it is going. We check the quantities and come back with a delivered price before you commit.