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Ballast Calculator

All-in ballast is how most concrete gets mixed on British sites: sharp sand and gravel already blended, so you only handle two materials instead of three. Enter the volume of finished concrete you need and pick your cement to ballast ratio — the calculator returns tonnes, bulk bags and cement.

Cement : ballast by volume16CementBallast+ water — mixed to a workable consistency
Ballast mix proportions
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Ballast and cement per cubic metre

Mix (cement : ballast) Use Ballast per m³ Cement per m³
1 : 5 Driveways, stronger slabs ~2.2 t ~15 bags (25 kg)
1 : 6 Footings, shed bases, general (≈C20) ~2.3 t ~13 bags (25 kg)
1 : 8 Lean mix, mass fill ~2.4 t ~10 bags (25 kg)

A bulk bag — the dumpy bag merchants deliver on a Hiab — holds about 850 kg. One of those with five bags of cement makes roughly 0.35 to 0.4 m³ of concrete at 1:6. Three bulk bags and 13 cement bags gets you to a cubic metre with a little spare.

Mixing it properly

  1. Measure by volume with a bucket, using the same bucket throughout. One of cement to six of ballast. A shovel is not a unit of measurement — shovel loads vary by 30 per cent depending on who is holding it.
  2. Dry-mix first until the colour is uniform grey with no streaks. Skipping this leaves pockets of unbound aggregate.
  3. Add water gradually, roughly half a bucket per bucket of cement. Stop when it holds a ridge without slumping.
  4. Place within 45 minutes and compact well. Air pockets are voids, and voids are where the strength goes.

Above about a quarter of a cubic metre, hire a mixer. Hand mixing beyond that produces inconsistent batches and a very long day.

Frequently asked questions

How much ballast for 1m³ of concrete?

Roughly 2.3 tonnes of all-in ballast plus 13 bags of 25 kg cement at 1:6 — about three 850 kg bulk bags.

How many bulk bags of ballast per cubic metre?

Three 850 kg bags covers a cubic metre of mixed concrete with a margin. Loose tipped ballast is usually cheaper per tonne if you have somewhere to put it.

What is the cement to ballast ratio?

1:6 for general concrete such as footings and bases, about C20 strength. 1:5 for something stronger, 1:8 for lean fill. Measured by volume, not weight.

Is ballast the same as sand and gravel?

Yes — all-in ballast is pre-blended sharp sand and gravel, typically up to 20 mm stone. Buying them separately lets you tune the mix; ballast saves handling. For separate quantities use the mix ratio calculator.

How much water for a 1:6 ballast mix?

Around 12 to 14 litres per 25 kg bag of cement, adjusted for how wet the ballast already is. After rain it will need considerably less.

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