Calculator
Formula used
Bottom width (base)
Wb = OD + 2·WS + 2·ST (if supported)
Wb = Wb · (1 + A)
Wb = Wb · (1 + A)
OD is pipe outside diameter, WS is working space each side, ST is support thickness each side,
and A is the added allowance percentage.
Top width (ground)
Supported: Wt = Wb
Sloped: Wt = Wb + 2·D·SR
Sloped: Wt = Wb + 2·D·SR
D is trench depth to bottom and SR is the side slope ratio (H:V).
Sloped excavations widen at the ground line.
Area and volume
Area = (Wb + Wt) / 2 · D
Volume per meter = Area · 1
Total volume = Volume per meter · Length
Spoil ≈ Total volume · Bulking factor
Volume per meter = Area · 1
Total volume = Volume per meter · Length
Spoil ≈ Total volume · Bulking factor
The calculator uses a trapezoid cross-section for sloped sides and a rectangle for supported excavations.
Confirm geometry when benches, steps, or layered soils are used.
Reminder: This tool supports planning and documentation.
Always follow project specs and local excavation safety requirements.
How to use this calculator
- Choose your unit system and enter the pipe outside diameter.
- Enter the depth to the trench bottom and select soil category.
- Select an excavation approach: sloped, shored, or trench box.
- Use Auto to apply planning suggestions for working space and slope.
- Add a small allowance percentage if tolerances are uncertain.
- Optionally enter length and bulking factor for spoil estimates.
- Press Calculate, then export CSV or PDF if needed.
Example data table
| Scenario | Pipe OD | Depth | Method | Working space/side | Slope (H:V) | Bottom width | Top width |
|---|---|---|---|---|---|---|---|
| Urban utility trench | 250 mm | 1.8 m | Sloped | 200 mm | 1.0 | 650 mm (25.59 in) | 4,250 mm (167.32 in) |
| Deep run with trench box | 400 mm | 2.4 m | Trench box | 300 mm | — | 1,208 mm (47.56 in) | 1,208 mm (47.56 in) |
| Small service line | 6 in | 6 ft | Shored | 8 in | — | 711 mm (28.00 in) | 711 mm (28.00 in) |
Tip: Run each scenario through the calculator to populate exact outputs for your project.