All 43 tools
Concrete & screed · ballast · cement
How much ballast and cement do I need?
Ballast and cement for mixing on site. Two methods are offered: proportioning by volume, which is what a mix ratio normally means, and the by-weight shortcut the old sheet used — which comes out about 20% richer on cement.
Measure it
Every box has its own unit next to it.
Change the unit beside any box and the number converts. The (i) beside each question says what the box wants and where the figure usually comes from. Anything marked per cent is a percentage of the quantity above it.
Check the rates
Rates and assumptions used
These are the figures the calculator works to. Change any of them and the order list updates — your merchant’s pack sizes and your own waste allowances beat the defaults every time.
Order list
The orange figure is the one you order to. Highlighted rows are the other numbers you order to. The small print under each row is the sum that produced it, so you can check it against your own take-off. Amber rows are warnings, not quantities.
How this one works
- Dry volume =
wet volume × dry-to-wet factor— dry materials shrink when mixed and wetted - By volume (standard):
cement volume = dry ÷ (ratio + 1), then × cement bulk density for the weight - By weight (the old sheet): ballast weight ÷ ratio = cement weight. Simpler, and richer
- Water is worked at the water-to-cement ratio — start drier than that and add to suit
The figures the calculator works to. Every one can be changed in step 2, and your merchant’s pack sizes and your own waste allowances beat these defaults every time.
| Rate | Default | Why |
|---|---|---|
| Ballast density | 1.7 t/m³ | All-in ballast, loose. The figure the old sheet used. |
| Cement bulk density | 1.44 t/m³ | Loose cement powder — only used on the volume method. |
| Dry-to-wet factor | 1.5 | Dry materials to finished concrete. 1.5 is the usual allowance. |
| Cement bag | 25 kg | |
| Ballast bulk bag | 0.85 t | |
| Water : cement | 0.55 | By weight. Lower is stronger and stiffer; 0.5–0.6 is the workable range. |
| Mixer batch | 90 L | Mixed concrete out of a 4/3 mixer per batch. |
| Shovel volume | 5 L | A builder’s shovel, heaped. |
A worked example
With the defaults the page opens on:
- How much concrete? 2.5 cubic metres
- Or how long is it? 0 metres
- How wide is it? 0 metres
- How deep is it? 0 metres
- Which mix? 1:6 — general C20
- Proportion by volume or by weight? Volume — standard practice
- How much spare for waste? 5 per cent
Materials
- Wet volume (with waste): 2.63 m³ — +5% waste
- Dry (loose) volume: 3.94 m³ — × 1.5 dry-to-wet
- Ballast: 5.74 t
- Ballast bulk bags: 7 bags — at 0.85 t
- Cement: 33 bags — = 810 kg, proportioned by volume
- Water (approx): 446 litres — at 0.55 water:cement — add to suit, do not drown it
Mixing
- Mixer batches: 30 batches — at 90 L of mixed concrete a batch
- Shovels of ballast per bag: 21 shovels — one 25 kg bag to 6 parts ballast, by volume
- Ballast per bag of cement: 177.1 kg
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
How much ballast and cement for 1 m³ of concrete?
At 1:6 by volume the calculator gives roughly 1.7 t of all-in ballast and 9 to 10 bags of cement per cubic metre, once the dry-to-wet factor of 1.5 is applied. Change the mix or the method and the page shows the difference.
What does "by volume" versus "by weight" mean?
A mix ratio like 1:6 normally means parts by volume: one bucket of cement to six of ballast. The older site sheet divided the ballast weight by the ratio instead, which gives about 20% more cement. Both are offered so you can match whichever your quote was priced on.
How much water goes in?
The calculator works water at a 0.55 water-to-cement ratio by weight. Start drier than that and add to suit - a wetter mix is weaker.
How many shovels of ballast per bag of cement?
For a 25 kg bag at 1:6 by volume, about 21 heaped shovels. The figure comes from the cement bulk density and a 5-litre shovel, both of which you can change.
Calculators for the same job
Doing this for a whole job rather than one wall? SiteLedger keeps the valuations, supplier statements, invoices and variations against the project they belong to.
Read before you order. These work out quantities, not structural design — spans, lintels, rebar and foundation depths need an engineer and Building Control sign-off. Waste allowances are defaults, not promises: awkward cuts, long runs and bad weather all eat more than 5%. Where a merchant sells whole packs, the figure is rounded up to whole packs.