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Groundworks · m³ · t · loads
How much muck will I dig out, and how many loads is that?
Dig volume, what it turns into once it is out of the ground, and how many lorries that is. Bulking is the bit that catches people out — a cubic metre of clay in the ground is a cubic metre and a third in the wagon.
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
Dig volume = L × W × D plus any extra pits or steps
Weight = dig volume × in-situ density — the density before it is disturbed
Bulked volume = dig volume × (1 + bulking %) — broken ground takes up more room
Grab and tipper loads go by weight because that is what the haulier charges; skips go by bulked volume because that is what fills the box
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
Grab lorry payload
14 t
Typical 8-wheel grab. Check with your haulier — some run at 12 t on soft island roads.
Tipper payload
18 t
8-wheel tipper. A 6-wheeler is nearer 12 t.
Skip volume (8 yd)
6.1 m³
An 8-yard builder’s skip. A 6-yard is 4.6 m³, a 12-yard is 9.2 m³.
Fill level of skip
85 %
Nobody fills a skip to the brim and they will not take it over the lip.
A worked example
With the defaults the page opens on:
How long is the dig? 12 metres
How wide is it? 8 metres
How deep is it? 0.9 metres
Any extra to dig out? 0 cubic metres
What is the ground? Topsoil / made ground
In the ground
Dig volume: 86.4 m³ — L × W × D + extras
Weight: 155.52 t — volume × 1.8 t/m³
Once it is out
Bulking: 25 % — how much it swells when dug
Bulked volume: 108 m³ — dig volume + 25%
Grab lorry loads: 12 loads— by weight: 155.5 t ÷ 14 t payload
Tipper loads: 9 loads — by weight, 18 t payload
8-yard skips: 21 skips — by bulked volume, filled to 85%
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
What is bulking and why does it matter?
Ground takes up more room once it is dug. Clay bulks by about 30%, so a cubic metre in the ground is a cubic metre and a third in the wagon. Skips are filled by bulked volume, so ignoring it under-orders skips.
Are grab loads worked by weight or volume?
By weight, because that is what the haulier charges against a payload. Skips are worked by bulked volume, because that is what fills the box. The calculator does both.
How heavy is a cubic metre of clay?
About 1.9 t in the ground. Topsoil is nearer 1.8, sand and gravel 2.0, rock 2.3. Picking the material sets the density and the bulking together.
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.
