Bedding & Spoil Calculator
Per-run accuracy. Per-run materials. Per-run bedding.

Most people picture bedding as just the layer of sand under the pipe. That is the single most common misunderstanding on a trench, and it leads to under-ordered material and under-priced runs.

The pipe is not just sitting on a layer. It is surrounded — material goes below it, up both sides, and over the top of it. That whole envelope around the pipe is the embedment. It is what actually supports the pipe and lets it carry load without deforming, so it has to be a controlled, compactable material placed and compacted in the right zones, not just tipped in.

Embedment is not always one material either. On many jobs you will have one material directly beneath the pipe and a different material around and above it — for example a bedding sand under the pipe and a graded aggregate as side support and overlay. So a single run can carry two embedment materials, in two quantities, and if you price it as one you will be wrong on both.

Above the embedment sits the trench fill — and this is the second thing people get wrong. They assume you just backfill with the material you dug out. You often cannot:

• If the excavated material is unsuitable — wet clay, oversized rock, organic material — it cannot go back in, and you have to bring in import fill.
• If the run is in a trafficable area or under a building, the fill above the embedment, up to the underside of the pavement, has to be an engineered import fill that can carry the load. Site-won spoil will not do.

That single decision — whether the fill above the pipe is your own excavated material or imported fill — can swing the cost of a run more than the bedding itself. It is the line an inexperienced estimator misses, and it is exactly the sort of thing we resolve on every job before we price it.

The calculator handles these as separate zones and materials so a mixed run comes out right. For the full picture on your job, send us the drawings.

For a full hydraulic estimate including a complete materials schedule, contact SNZ. We include bedding and trench fill quantities in every estimate we produce.

As a working rule, allow 300mm minimum cover from the top of the pipe to the finished surface in unpaved areas, and 500mm in paved areas subject to traffic loading. This calculator applies both requirements automatically — if you enter a depth that does not meet the minimum, the depth adjusts instantly and shows you the corrected value.

SNZ works to AS/NZS 3500 and the relevant authority spec on every civil stormwater estimate and hydraulic estimate we produce — the calculator is built on the same standard.

Spoil is the surplus that does not go back into the trench. It equals the volume displaced by what takes the native material's place: the pipe itself, plus imported bedding and embedment, plus imported trench fill or concrete encasement where used. Excavated native material that is reused as backfill is not spoil. This calculator does this automatically for each pipe run — enter the DN size, depth to invert and linear metres and total spoil is calculated instantly in both m³ and tonnes.

Trench width is taken as the pipe outside diameter plus a working clearance each side, so the pipe can be bedded and compacted properly. Your clearance may be set by the project specification. For government and rail projects SNZ includes complete material schedules with every estimate.

A truck & dog carries 32 tonnes (~23m³ loose). A rigid truck carries 14 tonnes (~10m³). This calculator shows both figures automatically based on your spoil volume — truck & dog for open sites with good access, rigid truck for restricted suburban or tight access sites.

Always confirm load capacities with your haulage contractor. Clean fill spoil is typically taken to fill sites, not tips — haulage cost is per load. SNZ includes excavation and spoil quantities in all high-rise residential and commercial hydraulic estimates.

For excavated clay being removed as spoil, use the loose or bulked density — typically 1.4 t/m³ for clay. Clay expands when excavated (bulking factor of approximately 20-30%) so the loose density is lower than the in-situ compacted density. This is the correct value for truck load estimation and is the default in this calculator.

Do not use compacted density for spoil disposal — it will overestimate your truck load requirements significantly.

For ordering embedment material from a supplier, use the compacted density — 1.8 t/m³ for crushed rock. DGB20 road base as trench fill is typically 2.0 t/m³ compacted. These are the correct values for supplier ordering — compacted density is how the material performs in the trench and how suppliers price it.

SNZ uses these exact density values in industrial, airport and rail project estimates where accurate material ordering is critical.

Yes — unlike dropdown-based calculators with fixed pipe size lists, this calculator accepts any DN size you type. DN100, DN375, DN1500, DN2400, DN3000 — all calculated correctly using the same formula. The trench cross-section diagram updates live to show the correct scale of your pipe relative to the trench.

SNZ has estimated large-diameter civil stormwater for shopping centres, airports and major government infrastructure projects nationally.

The calculator gives accurate theoretical quantities based on the dimensions and parameters you enter. Real quantities vary with soil conditions, pipe manufacturer tolerances, site conditions and contractor methodology — always add a contingency allowance of 10-15% for real project pricing.

For a fully priced, bankable estimate ready for tender submission, SNZ provides complete hydraulic estimates across all sectors and states — individually measured from your drawings, not benchmarked.

No account or subscription required. Three free calculations are available immediately with no login. After three uses a one-time registration is required — name, company and email address only. Once registered the calculator is unlocked permanently on your device at no cost.

Yes. The Share button copies a link that encodes your entire calculation — pipe sizes, depths, linear metres, pits, tanks and material settings. Anyone opening that link gets the calculator pre-filled with exactly what you entered. You can also export a branded PDF report or email the results to yourself directly.

SNZ contractors use this to share preliminary quantities with clients before formal budget pricing or full tender estimates.

SNZ estimates for every major construction sector across Australia — hospitals and healthcare, high-rise residential, commercial and retail, government infrastructure, schools and universities, industrial, fuel stations, shopping centres, airports, McDonald's and rail and train stations.

View our project case studies for real credentials across each sector — 420+ projects across NSW, VIC, QLD, SA, WA, NT and ACT.

Yes — this is exactly what SNZ does. The calculator gives you quantities for budgeting. SNZ gives you a fully priced, bankable hydraulic estimate ready for tender submission — every pipe, fitting and system individually measured and priced from your drawings.

15 years experience, 420+ projects. Available in Sydney, Melbourne, Brisbane, Perth, Adelaide, Canberra and Darwin. Request an estimate here or call 0451 404 645.

Trench width × depth × length gives you the excavation volume, which is what you dig. Spoil is different: it is only what does not go back in. So the spoil formula is pipe volume + imported bedding and embedment + imported trench fill or encasement. If all the excavated native goes back in, the spoil is just the pipe volume. Convert spoil to tonnes for disposal with the soil density, for example clay at roughly 1.4 t/m³.

The calculator above applies this formula to every pipe run automatically, using your project clearances, so you get the spoil in m³ and tonnes without doing the maths by hand. And if you want the whole job priced, not just the trench, that is what our hydraulic estimating service does.

Bedding is calculated in zones. Take the bedding thickness below the pipe (commonly 75mm), plus the embedment beside and above the pipe (commonly 100mm above), across the full trench width, multiplied by the run length, then subtract the volume the pipe itself displaces. Convert to tonnes with the material density, for example crushed rock at roughly 1.8 t/m³.

Doing that per pipe size across a whole job is fiddly, which is exactly what this calculator automates. Enter the size and length of each run and the bedding, embedment and trench fill quantities come back in seconds. If you also need the fixtures broken out for ordering, see our materials order list service.

For each pipe run, total the displaced volume: the pipe plus the imported bedding, embedment and any imported fill or encasement. Reused native backfill does not count. Then add pits, tanks and below-ground structures, which spoil their full excavation volume because the structure occupies the hole. The total is your spoil in cubic metres, and the soil density converts it to tonnes for disposal.

The fastest way is to enter your runs into the calculator above. It totals the spoil across every run, pit and tank, shows it in m³ or tonnes, and works out how many truckloads it means for your site access. On spoil-heavy jobs, our civil and stormwater estimating covers the full trench pricing.

Yes. Subsoil and agi drains do not follow standard bedding geometry, the whole trench is backfilled with aggregate around a slotted pipe. In the calculator, open the advanced settings on a pipe run and switch on subsoil drain mode. You set your own trench width and depth, choose the aggregate, and it calculates the aggregate quantity and the full trench volume as spoil.

The criteria used for the calculation are shown right in the panel, so you can check them against your drawings.

Yes. Real jobs rarely use one material everywhere. In the advanced settings of any run you can set that run's own embedment material, for example coarse sand on one run, crushed rock on another and DGB20 on a third, and its own trench fill, including stabilised sand and flowable fill.

The material breakdown section then groups the results by material, so you see the order quantity for each one separately. Flowable fill is always shown in cubic metres because it is ordered by volume, not weight.

Yes. The linear metre cells accept formulas the same way Excel does. Type 23+14.5+8 straight into the cell and it sums to 45.5 metres, so you can add up multiple runs of the same pipe size from your takeoff without a side calculation on a notepad. It pairs well with whatever takeoff software you measure in.

Both. One click switches every result between m³ and tonnes. The tonnes conversion uses the actual density of the material you have selected for each category, and each run can carry its own densities, so mixed-material jobs convert correctly rather than using one blanket figure.

The only exception is flowable fill, which is always shown in cubic metres because it is ordered like concrete, by volume.

Trench width is the pipe outside diameter plus the side clearance on each side of the pipe. The default side clearance is 100mm per side, and you can adjust it globally or per run in the advanced settings. That width flows through every calculation: bedding, embedment, trench fill and spoil.

If your project specification calls for a different clearance, change it and every quantity updates instantly.