Excavation and soil calculator

Pick the shape of the dig, punch in your measurements, and everything updates as you type. Trench covers footings, drainage runs and cable trenches. Pad covers site scrapes: a slab, a shed base, a deck footprint, stripping tired lawn. Post holes does the round-hole maths for a fence or pole build, times however many holes you are drilling.

Then tell it your soil and how you plan to cart the spoil. The soil type sets two numbers at once: how much the dirt swells when dug, and what it weighs. Both change the answer more than most people expect, which is what the next section is about.

Ground that has sat undisturbed for decades is packed tight. The moment a spade or a bucket breaks it out, air gets in between the lumps and the same dirt takes up more room. Earthworks people call it bulking, and they quote two volumes for every job: bank (measured in the ground) and loose (measured on the truck).

The swing depends on the soil. Published swell tables put clean sand and gravel around 14 percent, loam and topsoil around 20, dense clay around 35, and broken rocky ground anywhere up to 50 or more. So a tidy 3m³ trench in clay quietly becomes about 4m³ of spoil on the lawn. Skip that step and your skip, trailer plan and cleanfill budget are all a third short before you start.

The amateur estimate is volume only: measure the hole, hire a trailer, get surprised. The pro estimate runs three numbers in a row, and this calculator does the same:

• Bank volume: the hole itself. Length by width by depth, or the cylinder maths for holes.
• Loose volume: bank times the bulking factor. This is the quantity you cart and pay disposal on.
• Weight: bank volume times density. Clay runs around 1.8 tonnes per bank cubic metre, topsoil around 1.4, sand about 1.6, rocky ground 2 or more.

Weight is the one that bites, because a trailer fills by weight long before it looks full. A typical caged single-axle hire trailer is rated to about 680kg of load; that is roughly half a cubic metre of loose clay, sitting well below the cage rails. Heap it "full" and you are towing double the rating: illegal, uninsured if anything happens, and genuinely dangerous to stop. A tandem at about 1,600kg carries a touch over a cubic metre of clay. That is why this tool counts loads off the payload plate, not off the cage size.

One cubic metre of clay is about 1.8 tonnes. Moved by hand that is 35 to 45 wheelbarrow trips, every one of them dug, lifted, wheeled and tipped, and in real clay a fit person is doing well to dig and shift one to two cubic metres in a day. Your trench above might read as a tidy weekend and actually be a week of your back.

A small hire excavator changes the equation completely: what costs a labourer a day costs the machine well under an hour, and it stockpiles the spoil exactly where the trailer backs up to. The rough rule: under about a cubic metre in soft ground, shovels are honest work. Past two or three cubic metres, or anything in clay or rocky ground, the digger hire pays for itself in your first sore morning. If you are digging for concrete next, our concrete calculator picks up where this one stops.

Clean excavated soil goes to a cleanfill. The definition is stricter than the name suggests: cleanfills accept virgin natural material, meaning soil, clay and rock, plus inert material like brick or unreinforced concrete. They do not take green waste, stumps, treated timber offcuts, plasterboard, general rubbish, or anything from a site with a contamination history (old sheep dips, workshops, horticultural land). Charges are typically by the tonne or cubic metre and vary by region, so ring before you load.

Other honest options: a "clean fill wanted" listing (people genuinely want good soil for landscaping), keeping topsoil on site for garden beds because bought topsoil is not cheap, or a hired skip for small mixed loads, telling the skip company it is soil first, since many price dirt differently or refuse it. The expensive mistake is mixing: one load of clean soil with fence offcuts and a paint tin through it stops being cleanfill and starts being priced as general waste.