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Free groundworker calculator
Hardcore and excavation calculator: dig volume, skips, muck away and MOT Type 1
Work out the dig for a slab, base, drive or footing trench: how much comes out, how much it grows once it is loose, what it weighs, how many skips or grab loads that is, and how many tonnes of MOT Type 1, blinding and DPM go back in. Spoil is weighed at its in-ground density, skips are real UK sizes with their soil weight limits, and Type 1 is 2.1 tonnes per compacted cubic metre plus 10%.
What you need
Dig
- Excavation
- 6.00 m³12.0m² × 0.5m, solid in the ground
- Spoil to remove
- 7.80 m³ looseMixed soil and subsoil bulks by 30% once dugmaterialcalculator muck-away; digfill
- Spoil weight
- 9.9 tonnes1.65 t/m³ in the ground; bulking adds volume, not weightmaterialcalculator in-situ densities
- Skips
- 2 × 8-yard builder's skip (6.1 m³, ~8 t)weight governs: soil is heavy and a skip firm will not lift more than about 8 tonneslovejunk skip guide; materialcalculator
Fill
- MOT Type 1
- 4.16 tonnes150mm compacted at 2.1 t/m³ plus 10%: 0.35 t per m². Or 6 bulk bags (~800 kg). Whack it in 75mm layerstradecalculator Type 1: 2.1 t/m³ compacted
- Blinding sand
- 2 bulk bags (~800 kg)50mm of sharp sand over the Type 1 to protect the DPM, 1.06 tonnes at 1.6 t/m³ plus 10%
- DPM 1200 gauge
- 1 × 4 × 25 m roll (100 m²)includes 15% for 150mm laps and turning up at the edges; tape the laps
- Area
- 12.0 m²for the concrete calculator
Round up to whole packs and bags. Figures include the wastage you chose and match TradeCalc in the app.
For groundworkers: turn this into a quote
In the app, TradeCalc hands these quantities straight to ProQuote with your regional material prices, and the customer gets a branded PDF. Free to download.
Or claim your free profile link nowHow the maths works
- Excavation is length × width × depth, the solid volume in the ground before anything is disturbed. A trench uses the trench width instead of the plan width.
- Dug soil takes up more room than it did in the ground: topsoil bulks about 25%, mixed ground and clay 30%, sand 12%, chalk, rock and rubble 40% (materialcalculator muck-away; digfill). Weight is the solid volume × the in-ground density: topsoil 1.4, mixed 1.65, clay 1.85, sand 1.6, chalk or rock 2.0, rubble 1.9 tonnes per m³. Bulking does not add weight.
- Skips are real UK sizes: a 6-yard is 4.6m³ and an 8-yard builder's skip 6.1m³ (1yd³ ≈ 0.76m³), but on soil they are weight-limited to about 6 and 8 tonnes, so the count is whichever of volume and weight needs more skips (lovejunk; materialcalculator). Grab lorries take 8 to 10 tonnes (4-wheel), 12 to 13 (6-wheel) or 14 to 16 (8-wheel).
- MOT Type 1 is ordered by the tonne at 2.1 tonnes per compacted cubic metre plus 10% (tradecalculator). That already covers compaction, so there is no separate 1.3 factor: at 150mm it is 0.35 tonnes per m², and a bulk bag of about 800kg does roughly 2.3m². The block paving and extension calculators use the same figure.
- Blinding is 50mm of sharp sand at 1.6 tonnes per m³ over the Type 1 to protect the DPM, or 50mm of GEN0 concrete blinding where a footing or slab needs a clean, level formation (Cemex).
- The DPM is 1200 gauge polythene in 4 × 25m (100m²) or 4 × 12.5m (50m²) rolls, with 15% added for 150mm laps and turning up the edges. The old 15m² roll figure was for 1F felt, not DPM.
Worked example
A 4m × 3m base dug 500mm deep in mixed ground is 6m³ of excavation, which bulks up to 7.8m³ and weighs about 9.9 tonnes, so two 8-yard skips (weight governs). Filling back with 150mm of Type 1 takes 4.16 tonnes, 6 bulk bags, plus 2 bulk bags of blinding sand and 1 roll of DPM.
Questions people ask
How many tonnes of MOT Type 1 do I need per square metre?
0.35 tonnes per m² at 150mm compacted, including 10% for wastage, so a bulk bag of about 800kg covers roughly 2.3m². At 100mm it is 0.23 tonnes per m² and at 200mm 0.46. Type 1 is 2.1 tonnes per cubic metre once compacted; loose in the bag it is nearer 1.8 to 2.
Why is the spoil more than the hole, and why does it not weigh more?
Soil is compacted in the ground and loosens when it is dug: mixed ground and clay grow by about 30%, sand only 12%, chalk and rock up to 40%. The weight does not change, so tonnage is the solid volume times the in-ground density, about 1.65 tonnes per m³ for mixed ground and 1.85 for clay.
Skip or grab lorry?
For more than one skip's worth, a grab is usually cheaper per tonne and quicker, as long as the arm can reach the pile from where it parks. An 8-wheel grab takes 14 to 16 tonnes or 10 to 12m³; a 4-wheeler about 8 to 10 tonnes. Skips are weight-limited on soil: an 8-yard skip holds 6.1m³ but the firm will only lift about 8 tonnes.
How deep should I dig for a concrete base?
Add up the layers: 150mm Type 1, 50mm blinding and 100 to 150mm of concrete gives 300 to 350mm, plus a bit more if you want the slab sitting below the damp course. Footings are a different job; Building Control sets those depths, and the concrete calculator has a strip footing mode.
Can I use crushed concrete instead of MOT Type 1?
Recycled Type 1 (crushed concrete or brick, sometimes sold as 6F2 or crush and run) is fine for most bases and drives and is often cheaper. It is graded to the same spec, so the tonnage here still applies.
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