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Groundworks · m³ · t
How much concrete goes in a strip foundation?
Trench dig, concrete fill and the muck away off it, from the total run of footing. Depth and width come off the engineer’s detail — this works out what it costs to fill, not whether it is deep enough.
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
Trench dig = run × width × dig depth
Concrete = run × width × concrete depth. For trench fill, set concrete depth close to dig depth
Order quantity is rounded up to the batching plant’s step
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
Spoil density
1.9 t/m³
In-situ weight of what you dig out.
Bulking
30 %
How much the spoil swells once it is out of the trench.
Concrete full load
6 m³
A full mixer. Part loads usually carry a surcharge.
Net concrete: 16.56 m³ — run × width × concrete depth
Waste allowance: 7.5 %
Order quantity: 18 m³— rounded up to 0.25 m³
Full loads: 3 loads — at 6 m³ a load
Weight on the ground: 43.2 t — at 2.4 t/m³
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 concrete does a strip foundation take?
Run × width × concrete depth, plus waste, rounded up to the batching step. For 46 m of 600 mm trench with 600 mm of concrete that is about 17.75 m³ to order at 7.5% waste.
What is the difference between strip and trench fill?
A strip footing has 225-300 mm of concrete with masonry built up off it; trench fill takes the concrete to within about 150 mm of ground level. In the calculator, set the concrete depth close to the dig depth for trench fill.
How deep should the trench be?
That is the engineer’s and Building Control’s call - 900 mm is a common minimum, deeper near trees. This calculator prices the dig and the fill for the depths on the drawing; it does not decide them.
Why does it flag when the concrete is deeper than the dig?
Because one of the two figures is wrong. It is the commonest transposition on a take-off, so the page says so rather than silently ordering the wrong amount.
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.
