Free civil tool · Metric · No signup
Trench Calculator
Measure a rectangular trench, then separate excavation, bedding, pipe-zone aggregate, backfill and loose spoil.
Example inputs are editable. Use your project values. Enter 0 where no optional allowance is intended; blank fields pause the calculation.
Your inputs
Your results
- Excavation (bank)
- 120 m³
- Bedding
- 12 m³
- Pipe displacement
- 7.07 m³
- Pipe-zone aggregate above bedding
- 28.93 m³
- Upper backfill (in-place)
- 72 m³
- Excavated volume to export (bank)
- 48 m³
- Spoil to cart (loose)
- 48 m³
Calculation breakdown
Excavation = 100 × 0.8 × 1.5 = 120 m³
Bedding depth = 150 mm ÷ 1000; pipe OD = 300 mm ÷ 1000
Upper backfill = 120 − 12 − 28.93 − 7.07 = 72 m³
Loose export = 48 × (1 + 0/100) = 48 m³
Displayed values are rounded. The calculation uses unrounded inputs.
These free results do not automatically save or sync to a Fieldlink job.
How it works
- Convert mm to m by dividing by 1000
- Excavation = L × W × total depth
- Bedding = L × W × bedding depth
- Pipe displacement = π × (OD/2)² × L
- Pipe-zone aggregate = L × W × (OD + cover above crown) − pipe displacement
- Upper backfill = excavation − bedding − pipe-zone aggregate − pipe displacement
- Export bank volume = excavation − reused upper backfill, or all excavation
- Loose export = export bank volume × (1 + bulking/100)
- Volume-only loads = ceiling(loose export ÷ truck bin capacity)
Worked example
100 m × 0.8 m × 1.5 m = 120 m³ excavation. With 150 mm bedding, 300 mm OD and 150 mm cover: bedding 12 m³, pipe displacement 7.07 m³, pipe-zone aggregate 28.93 m³, upper backfill 72 m³. Reuse mode exports 48 m³ bank before any bulking allowance.
Assumptions and practical notes
Uniform rectangular section, vertical sides and one circular pipe run. Zero cover still includes aggregate beside the pipe up to its crown. Reuse mode assumes suitable excavated material replaces upper backfill one-for-one in bank/in-place volume; no compaction factor is inferred. Export-all mode requires imported upper backfill. A zero bulking default is an explicit no-allowance example, not a soil recommendation.
Use drawings and specifications for final quantities. Batters, over-dig, shoring, multiple pipes and unsuitable-material replacement are not modelled. Check truck payload separately.
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Price the wider scope with takeoffs, labour, plant and material rates.