Cable Trench Volume Calculator

Trench Inputs

Project name

Used for report file names.

Input units

All dimensions below use this unit.

Trench shape

Trapezoidal uses a per-side H:V slope ratio.

Length (L)

Centerline trench length.

Bottom width (B)

Clear excavation width at base.

Depth (D)

From finished grade to trench bottom.

Side slope (H:V per side)

Example: 0.5 means 0.5H:1V on each side.

Over-excavation depth

Extra depth for soft spots or trim allowance.

Parallel trenches

Multiply volumes for multiple runs.

Materials and Adjustments

Bedding thickness

Set to zero if not used.

Bedding side clearance

Adds clearance on both sides for bedding width.

Soil swell factor (%)

Used to estimate loose spoil volume.

Backfill compaction factor (%)

Loose required = compacted ÷ (factor/100).

Waste / contingency (%)

Applied to all reported volumes.

Round results (decimals)

0–6 decimals.

Optional Duct and Encasement

Duct count (cylinders)

Used as displacement inside the trench.

Duct outside diameter

Set to zero if not applicable.

Concrete encasement thickness

Prismatic volume, thickness × width × length.

Concrete encasement width

Use with thickness to include encasement volume.

Reset

Example Data Table

Scenario	Shape	L (m)	B (m)	D (m)	Slope	Waste (%)	Excavation (m³)
Urban LV cable trench	Rectangular	30	0.45	0.90	0.00	5	12.758
Road crossing with side slopes	Trapezoidal	20	0.60	1.20	0.50	7	20.196
Shallow trench for controls	Rectangular	15	0.30	0.60	0.00	3	2.781

Example excavation values include the shown waste allowance.

Formula Used

Cross-sectional area

Rectangular: A = B × D_eff
Trapezoidal: Top width T = B + 2 × s × D_eff
Trapezoidal: A = (B + T) ÷ 2 × D_eff
U-shaped: A ≈ (B × (D_eff − r)) + (πr² ÷ 2), r = B/2

Volumes and factors

Excavation: V_exc = A × L × n
Bedding: V_bed = (B + 2c) × t × L × n
Duct displacement: V_duct = (π(OD/2)²) × L × count
Backfill (compacted): V_bf = V_exc − V_bed − V_enc − V_duct
Loose spoil: V_loose = V_exc × (1 + swell%)
Loose backfill needed: V_bf,loose = V_bf ÷ (compaction%/100)
Waste applied: V_final = V × (1 + waste%/100)

D_eff includes over-excavation. s is the per-side horizontal-to-vertical slope ratio. The calculator converts everything to meters internally.

How to Use This Calculator

Select the input units and trench shape.
Enter length, bottom width, and depth using your chosen units.
For trapezoidal trenches, set the side slope ratio (H:V per side).
Add bedding thickness and clearance if bedding is used on site.
Enter swell, compaction, and waste values that match your method statement.
Optionally include ducts and encasement to refine backfill quantities.
Click Calculate. Then download CSV or PDF for records.