Excavation calculator

DIY complexity

Advanced

Manual digging for a small project is physically demanding but achievable; the real risk is not technical skill but locating buried services and managing unstable trench sides safely.

Introduction

This calculator estimates how much soil or spoil will be removed and need hauling away when digging a foundation trench, a garden pond, a swimming pool, a service trench or a sub-base excavation — it is a removal and disposal estimate, not a material purchase like the other bulk calculators in this family. The key difference from ordering gravel or topsoil is direction: instead of buying and placing material, you are digging material out and taking it off site, and the volume you actually have to haul is larger than the hole you dug. Soil that sits undisturbed in the ground (bank volume) expands once it is dug up and loosened (loose or bulked volume), because the excavation process introduces air gaps between particles that were previously packed tight — this bulking or swell factor is often 20-30% or more depending on soil type, with clay typically swelling more than sand or gravel. Before any digging begins, buried services such as gas, water, electricity, telecoms cables and drains must be located and marked by the relevant utility locate service — this is a safety requirement, not a detail this calculator can check for you. The tool sums the area and depth of one or more measured zones into a bank volume, applies your chosen waste allowance and bulking percentage to estimate the loose volume to be hauled, converts that to weight using an editable soil density, and rounds up to a skip size or truck-load count against your hauler's minimum load, so you can size disposal and estimate cost.

Quick answer

For a 12 m² foundation trench dug 80 cm deep with a soil bulk density of 1700 kg/m³ and 25% bulking (swell), the bank volume is 9.6 m³, the loose volume to haul away is about 12.0 m³, and the estimated weight is about 20,400 kg (≈20.4 t) once bulking is applied to the loose volume.

Calculation methodology

01Before measuring or digging, have buried services (gas, water, electricity, telecoms, drains) located and marked by the relevant utility service — this is a safety step that must happen regardless of what the calculator says.
02Measure each area to be excavated as one or more zones (rectangle, circle, triangle, trapezoid or a hand-drawn outline) and enter the dig depth for each; note that a real trench with sloped or battered sides for safety will not match a perfect rectangular prism, so treat the plan-area figure as an approximation of the top opening.
03Sum the net area of all zones and multiply each by its own depth to get the bank (in-place, undisturbed) volume — the volume of the hole itself, before anything is dug.
04Apply a waste percentage for over-dig and irregular trench edges, then apply a bulking (swell) percentage separately, because loosened soil always occupies more space than it did packed in the ground.
05Convert the resulting loose volume to weight using the bulk density of the specific soil type being removed, since clay, sand, topsoil and rocky ground differ substantially in density and swell behaviour.
06Round the weight up to whole skip loads or truck loads, respecting the hauler's minimum load and any tipping or disposal fee, and compare the disposal cost options.

Formulas

loose_volume_m3 = Σ(area_i × depth_i) × (1 + waste) × (1 + bulking)

Every measured zone's net area is multiplied by its own dig depth and the results are added into a bank (in-place) volume — the physical size of the hole. That bank volume is inflated for over-dig waste and, critically, for bulking (swell): the same soil, once dug and loosened, spreads out and occupies more space than it did compacted in the ground, so the loose volume you must haul away is always larger than the hole you dug.

Variables

area_i = net plan area of zone i (m²)
depth_i = dig depth entered for zone i (m)
waste = over-dig and irregular-edge allowance (%)
bulking = swell of loosened soil versus its in-place (bank) volume (%)
loose_volume_m3 = total loose volume to be hauled away (m³)

Rounding rule: Neither the bank volume nor the loose volume is rounded at this stage; rounding only happens once weight is converted into whole skip or truck loads.

Limitation: This treats each zone as a perfect rectangular prism at the entered depth; it does not model battered (sloped) trench sides required for excavation safety at depth, which increase the actual bank volume beyond a simple area-times-depth figure — measure and add that extra volume as its own zone for a deep or unsupported trench.

weight_kg = loose_volume_m3 × density_kg_m3 × (1 + moisture); loads = ceil(weight_kg ÷ load_kg); truck_t = max(minimum_t, ceil(weight_kg ÷ 100) ÷ 10)

Loose volume is converted to weight using the bulk density of the specific soil or spoil type being removed, then increased for moisture if the ground is wet. The weight is rounded up to whole skip or container loads for small jobs, and separately rounded up to the nearest 0.1 tonne for truck haulage, with the hauler's minimum load enforced as a floor.

Variables

density_kg_m3 = bulk density of the loose soil or spoil type (kg/m³)
moisture = weight increase for wet ground at the time of digging (%)
load_kg = capacity of one skip or container
minimum_t = hauler's minimum load for truck removal (t)
truck_t = truck haulage quantity to book (t)

Rounding rule: Skip or container loads are always rounded up to a whole unit; truck haulage tonnage is rounded up to the nearest 0.1 t and then raised to the hauler's minimum load if that minimum is higher.

Limitation: 1700 kg/m³ is an editable example for a general soil, not a fixed constant — actual density and swell behaviour depend heavily on soil type (clay, sand, loam, rocky ground) and moisture at the time of digging, so confirm both figures against a site assessment or your groundworks contractor before booking disposal.

Inputs that matter

Dig depth per zoneDrives bank volume linearly, and a trench's real depth often needs to include an allowance for a sub-base or bedding layer beneath the structure, not just the visible finished depth.
Bulking (swell) percentageLoosened soil always occupies more space than the same soil in the ground — leaving this at zero understates the volume that actually has to be loaded and hauled, sometimes significantly for clay-heavy ground.
Soil type and bulk densityClay, sand, loam, topsoil and rocky ground differ substantially in both density and how much they swell once dug, so a figure taken from one soil type should not be reused for another without checking.
Buried servicesNot an input the calculator asks for, but the single most important safety check before any digging starts — utilities must be located and marked first, independent of anything this tool estimates.
Battered (sloped) trench sidesA trench with sides sloped back for safety at depth has more bank volume than a simple rectangular prism of the same footprint and depth; measure and add that extra volume separately if it applies.
Hauler minimum load and site accessSmall dig-out jobs may not reach a truck's minimum load, making a skip more economical, while large jobs need enough vehicle access for repeated truck visits — access is not something this tool checks.

Worked examples

Foundation trench for a 20 m² extension, 12 m² dug area

Foundation trenches for a 20 m² single-storey extension: 12 m² of actual trench footprint, 80 cm dig depth, general soil bulk density 1700 kg/m³, 5% waste, 25% bulking for this clay-loam ground.

Bank volume = 12 × 0.80 = 9.6 m³. With 5% waste and 25% bulking: 9.6 × 1.05 × 1.25 = 12.6 m³ loose volume. Weight = 12.6 × 1700 = 21,420 kg (≈21.42 t).

9.6 m³ is the physical size of the trench being dug; 12.6 m³ is the loose, bulked volume that actually has to be loaded and hauled away — noticeably more than the hole itself, purely because dug soil takes up more room than undisturbed ground. Skip or truck numbers should be sized against the 12.6 m³ / 21.42 t figure, not the 9.6 m³ bank volume.

⚠ Before digging this trench, buried services along its route must be located and marked by the relevant utility service — this is a safety requirement independent of the volume calculation and is not something the calculator verifies.

Garden pond excavation, 6 m² at 100 cm depth

A garden pond dug into loamy soil: 6 m² zone, 100 cm depth, bulk density 1700 kg/m³, 5% waste, 25% bulking, skip capacity 1000 kg each, hauler's minimum truck load of 5 t.

Bank volume = 6 × 1.00 = 6.0 m³. With 5% waste and 25% bulking: 6.0 × 1.05 × 1.25 = 7.875 m³ loose volume. Weight = 7.875 × 1700 = 13,387.5 kg (≈13.39 t). Skips (1000 kg): ceil(13,387.5 ÷ 1000) = 14 skip loads. Truck: needed 13.39 t is below the 5 t minimum per load only if a single load is booked below capacity — here it exceeds the 5 t minimum, so truck_t = ceil(13,387.5 ÷ 100) ÷ 10 = 13.4 t across multiple truck loads.

A modest 6 m² pond footprint still produces over 13 tonnes of spoil to remove once bulking is applied — this is why even small excavation projects often need multiple skip collections or several truck visits, not a single load. Comparing 14 skips against multiple truck loads lets you weigh site access and cost before committing.

⚠ 25% bulking is an editable planning assumption for loamy soil, not a guaranteed figure — sandy soil typically swells less and dense clay can swell considerably more, so confirm the expected swell factor for the actual ground conditions before booking disposal capacity.

Patio sub-base excavation and disposal cost, 30 m²

Excavating a 30 m² patio area down to sub-base level: 25 cm dig depth, bulk density 1700 kg/m³, 5% waste, 25% bulking. Skip hire costs 220 per 1000 kg skip; truck haulage costs 45 per tonne plus a 60 call-out fee, with a 5 t hauler minimum.

Bank volume = 30 × 0.25 = 7.5 m³. With 5% waste and 25% bulking: 7.5 × 1.05 × 1.25 = 9.84 m³ loose volume. Weight = 9.84 × 1700 = 16,734 kg (≈16.73 t). Skips: ceil(16,734 ÷ 1000) = 17 skips → 17 × 220 = 3740. Truck: ceil(16,734 ÷ 100) ÷ 10 = 16.8 t → 16.8 × 45 + 60 = 816.

Removing this sub-base spoil in 1000 kg skips would cost roughly 3740, while a bulk truck haulage booking at 16.8 t comes to about 816 including the call-out fee — truck haulage is clearly cheaper once the load comfortably clears the 5 t minimum, provided the site has room for a truck to access and load directly. The calculator surfaces both totals so the choice is based on cost and access together, not habit.

⚠ Changing the selected currency only changes the displayed symbol — it does not convert 220, 45 or 60 into a different currency's equivalent value. Enter current local hauler or skip-hire prices in the currency you have selected, and separately confirm any tipping or landfill tax that applies to the spoil type being disposed of.

Reading the results

The result panel separates the plan area you measured, the bank (in-place) volume of the hole itself, the loose volume after waste and bulking, the estimated weight, and the final whole-unit disposal quantity in both skip loads and truck tonnage — each figure is larger than the last for a specific reason: waste, then bulking, then the rounding needed to book a whole load. Skip cost and truck cost are shown side by side with the lower highlighted, so you can weigh price against site access before booking, since the tool cannot tell whether a truck can actually reach your excavation.

Common mistakes

Ordering disposal capacity for the bank (in-place) volume of the hole and forgetting the bulking allowance — the loose spoil to be hauled away is always larger than the hole itself, sometimes by a quarter or more.
Assuming a trench is a perfect rectangular prism at the entered depth, when safety regulations often require battered (sloped) or stepped sides at depth, which increase the actual volume of ground disturbed beyond a simple area-times-depth figure.
Digging before buried services — gas, water, electricity, telecoms cables, drains — have been located and marked by the relevant utility service; this is a safety-critical step the calculator cannot verify or substitute for.
Using one soil type's bulking percentage for a different type of ground — clay typically swells more than sand or gravel once dug, so a swell factor taken from one job site should not be assumed to apply to another.
Ignoring disposal or tipping fees and vehicle access constraints when comparing skip and truck options — the cheaper haulage rate on paper is irrelevant if a truck cannot physically reach or turn around at the excavation.
Not accounting for groundwater or drainage complications that can appear once digging starts, which this tool does not estimate and which can change both the timeline and the disposal weight if the spoil comes out wet.

Adapting to your country

Utility locate services, disposal regulations and permitted spoil handling vary significantly by country — some regions require a licensed carrier and waste transfer documentation for any soil leaving a site, while others allow informal disposal for small garden projects; confirm the applicable rule locally before committing to a removal plan. Skip and container sizes are typically sold by volume (e.g. cubic yards or litres) in some markets and by weight capacity in others, so check which unit your local hauler quotes before comparing options. Soil bulk density and bulking behaviour also vary by regional soil type — a site assessment or local groundworks contractor is a more reliable source than a generic average for anything beyond a small garden dig. Selecting a different currency changes only the displayed symbol — enter a current local hauler or skip-hire price for an accurate cost estimate, and confirm any tipping, landfill or environmental levy separately since it is not built into the calculator's cost output.

Limitations and verification

This calculator produces a planning estimate of volume, weight and disposal quantity — it is not a groundworks design, a structural or geotechnical survey, or a contractor quotation. It does not detect, verify or replace the mandatory step of locating buried services (gas, water, electricity, telecoms cables, drains) before digging; that must be arranged with the relevant utility locate service regardless of anything calculated here. It does not assess vehicle access for skip or truck collection at your specific site, and it does not model groundwater ingress, drainage complications, unstable ground, or the shoring and battering requirements that a real excavation at depth may need — those depend on site-specific conditions and should be confirmed with a groundworks contractor or geotechnical assessment before digging begins. Always treat the bulking percentage and soil density as editable planning assumptions for the soil type you expect, and adjust them once actual ground conditions are known.

Last reviewed: 2026-08-25

Frequently asked questions

Why is the loose volume to haul away larger than the hole I dug?

Because undisturbed soil in the ground (bank volume) is tightly packed, while the same soil once dug and loosened (loose or bulked volume) has air gaps between the particles and takes up more space — a bulking or swell factor of 20-30% or more is typical, and clay generally swells more than sand or gravel.

Do I need to locate buried services before using this calculator?

Yes, always, before digging — regardless of what this calculator estimates. Locating and marking gas, water, electricity, telecoms and drainage services is a safety requirement handled by the relevant utility locate service, not something this tool checks.

Does the calculator account for sloped or battered trench sides?

No. It treats each zone as a simple rectangular prism at the entered depth. A trench that requires battered or stepped sides for safety at depth has more actual volume than that simple figure, so measure and add the extra volume as its own zone if it applies to your dig.

Is the bulking percentage the same for every soil type?

No. Bulking varies significantly by soil type — clay generally swells more once dug than sand or gravel, and moisture content also affects the figure. Confirm an appropriate percentage for your actual ground conditions rather than reusing a generic default.

Does this calculator estimate the cost of a full excavation project?

It estimates the volume, weight and disposal quantity of the material removed, plus skip or truck haulage cost if you enter pricing. It does not estimate labour, machinery hire, shoring, dewatering or reinstatement costs.

Can this tool tell me if a truck can access my site?

No. Vehicle access, turning space and any restrictions on the route to the disposal point must be checked on site or with your hauler — the calculator only sizes the volume and weight to be moved.

Does changing currency convert the price I entered?

No. Changing currency only changes the display symbol and formatting; enter current local hauler, skip-hire or tipping prices in the currency you select.

Is the result enough to book disposal without any further checks?

No. It is a planning estimate. Confirm buried services have been located, verify the soil type and expected bulking with a site assessment or contractor, and check site access and any tipping fees before booking removal.

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