28 free tools · 25 site calculators plus HAV, 6×6 risk & accreditation · no sign-in · guidance only
All 28 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.
1
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.
2
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.
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
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: 6.58 t
Ballast bulk bags: 8 bags — at 0.85 t
Cement: 4 bags— = 93 kg, proportioned by volume
Water (approx): 51 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: 1,770.8 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.
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.
