The most accurate free trench calculator in Australia — calculates bedding, embedment, trench fill and spoil removal quantities for every pipe run independently. Per-run depth, per-run soil type, per-run bedding overrides, automatic AS/NZS 3500 compliance, formula entry in cells, mixed-material tonnes conversion, subsoil and agi drain mode, truck load estimates and live trench diagram. Engineering accuracy a generic calculator cannot provide.
Each pipe run has its own soil type, embedment material and trench fill material. Mixed-material jobs calculate correct weighted tonnes — run 1 in clay, run 2 in sand, totalled accurately. No other free tool does this.
Type 23+14.5+8 directly into any linear-metre field. Sum, subtract, multiply, divide. No more sitting with a separate calculator totalling runs before entry.
Bedding below, bedding above and side clearance override globally or per run. DN100 at 75mm bed and DN1500 at 150mm bed — both correct in the same job. Advanced Bedding Options on every row.
Estimating a subsoil or agi drain? Switch any pipe run to subsoil mode and set your own trench width and depth — the whole trench is backfilled with single-size aggregate or crushed rock around the pipe. Spoil and aggregate quantities calculated correctly for drainage trenches that do not follow standard bedding geometry.
Minimum cover checked automatically — 300mm unpaved, 500mm paved. Depth adjusts instantly if required, with a clean inline notification. No manual checking needed.
Three separate density categories — loose/bulked for spoil disposal, compacted for embedment ordering, compacted for trench fill. Each with multiple material options. The way engineers actually think.
Cross-section diagram scales live with your pipe size — pipe outer wall, embedment, trench fill, side clearance arrows all reposition dynamically. See exactly what you are estimating.
Spoil removal loads for truck & dog (32t, ~23m³) and rigid truck (14t, ~10m³). Open and restricted access sites calculated separately. Disposal logistics built in.
Branded PDF, email to yourself or copy a shareable link that pre-fills the entire calculation for colleagues. Job reference field on every export.
No credit card, no subscription, no software. Three free calculations then a one-time registration. Used daily by Australian plumbing contractors.
23+14.5+8 directly into the cells. Add as many pipe sizes as the job needs.Real jobs have multiple pipe sizes through multiple soil types. Run 1 may sit in sandy loam at 1.5 t/m³. Run 2 may be in clay at 1.4 t/m³. Generic calculators apply one density to the whole job and produce a wrong total. SNZ’s calculator handles each run independently, converts each volume to tonnes using its own material density, and totals the weighted figures correctly.
Same logic for embedment and trench fill — coarse sand, crushed rock, DGB20, road base. Each run carries its own material. The tonnes figure you see is the tonnes you actually need to order. This is what separates an estimating tool from a marketing widget.
Subsoil and agi drains break the standard bedding model entirely — a narrow trench fully backfilled with aggregate around a slotted pipe. Subsoil drain mode lets you set the trench width and depth directly and calculates the aggregate and spoil for that geometry, so drainage trenches are estimated as accurately as standard pipe runs.
AS/NZS 3500 minimum cover — 300mm unpaved, 500mm paved — applied automatically. Bedding below defaults to 75mm, above to 100mm, side clearance to 100mm. Spoil density defaults to clay (1.4 t/m³ loose). Embedment defaults to crushed rock (1.8 t/m³ compacted). Trench fill defaults to DGB20 road base (2.0 t/m³ compacted). All values overridable globally or per pipe run.
Calculate excavation volumes for pipes, pits and below-ground structures. Built on AS/NZS 3500 standards.
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Pit depths use avg depth to IL. Defaults to 1.0m if not entered.
Line-by-line results appear here as you enter values above.
Every pipe, pit, GPT, OSD system and civil reinstatement item individually measured from your actual drawings. Submission-ready. Defensible. Within 1 week for standard civil stormwater scopes.
Real questions from contractors using the calculator — answered honestly. Need a full hydraulic estimate? Call 0451 404 645 or send your plans and we will respond within a few hours.
Pipe bedding is the granular material placed directly around the pipe — below it (bedding layer), beside it (haunching) and above it to 300mm (initial backfill). Trench fill is everything above the embedment zone up to the finished surface. Bedding is typically imported crushed rock or DGB20. Trench fill is usually compacted native material or road base.
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/NZS 3500 requires 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 applies AS/NZS 3500 to 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 calculated from the pipe OD plus side clearances as per AS/NZS 3500. 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 — 300+ 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, 300+ projects. Available in Sydney, Melbourne, Brisbane, Perth, Adelaide, Canberra and Darwin. Get a quote 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 AS/NZS 3500 compliant depths for each pipe size, 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.
The calculator gives you quantities. SNZ gives you a fully priced, bankable estimate ready for tender — delivered fast.