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Groundworks · t · bags
How much MOT Type 1 do I need?
MOT Type 1 or scalpings to a finished compacted depth. Order it by weight — the loose heap that arrives is about a quarter bigger than the hole it ends up filling.
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
- Compacted volume =
area × finished depth - Order weight =
compacted volume × density × (1 + waste %) - Loose volume =
compacted volume × loose factor— what you need room to tip
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 |
|---|---|---|
| Compacted density | 2.1 t/m³ | MOT Type 1 compacted. Scalpings run about 1.9, recycled Type 1 nearer 1.8. |
| Loose-to-compacted factor | 1.25 | Loose material shrinks by roughly a quarter when it is whacked down. |
| Bulk bag weight | 0.85 t | A standard merchant bulk bag. Some sell 0.8 t, a few sell a full tonne. |
A worked example
With the defaults the page opens on:
- How long is the area? 10 metres
- How wide is it? 4 metres
- Any odd bits to add on? 0 square metres
- How deep once compacted? 150 millimetres
- How much spare for waste? 5 per cent
Sub base
- Area: 40 m² — L × W + extra area
- Compacted depth: 150 mm
- Compacted volume: 6 m³ — area × depth
- Waste allowance: 5 %
- Order weight: 13.23 t — volume × 2.1 t/m³, +5%
- Bulk bags: 16 bags — 13.2 / 0.85 tonnes a bag
- Loose volume delivered: 7.5 m³ — × 1.25 — leave room for the heap
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
How many tonnes of Type 1 per square metre?
At 150 mm compacted depth and 2.1 t/m³, about 0.33 t per square metre before waste. The calculator multiplies area by depth by density and adds your waste allowance.
What depth of sub base do I need?
The hints in the calculator give the common figures: 100 mm for a footpath, 150 mm for a drive, 250 mm or more for vehicles over 3.5 t. The right depth for your ground is a design decision; this works out the quantity for the depth you choose.
Why is the delivered heap bigger than the hole?
Loose material compacts by about a quarter when it is whacked down. The calculator shows the loose volume you need room for as well as the compacted volume you are paying to fill.
How many bulk bags is that?
The order weight divided by the bag weight, rounded up. The default is a 0.85 t bag; some merchants sell 0.8 t, a few a full tonne - set it to what yours sells.
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.