Sitework quantity calculator
Manhole Excavation & Backfill Calculator
Calculate the earthwork around a circular manhole from known excavation and outside structure dimensions. The result separates bank excavation, bedding, structure displacement, backfill and loose spoil.
Calculate manhole excavation & backfill quantities
This manhole excavation calculator finds the volume of a circular pit, subtracts the manhole structure and bedding from the space to be refilled, and reports bank excavation, backfill and loose spoil separately.
Formula: Backfill volume = excavation volume − manhole outside displacement − bedding volume. Loose spoil = bank excavation × (1 + entered swell percentage).
Use it for manhole excavation volume, manhole backfill quantity, manhole pit cubic yards and spoil takeoffs.
Step 1
Enter project dimensions
Use dimensions from the applicable drawing, specification or field takeoff. Switch between US / Imperial and metric at any time; entered dimensions are converted automatically.
Step 2
Quantity result
Bank excavation is in-place volume. Loose spoil applies the entered swell percentage. Backfill is a geometric balance and does not add a compaction factor unless explicitly represented by an input.
Worked example
The example below uses the calculator's starting dimensions so the inputs and outputs are visible to searchers and can be checked independently.
Example inputs
| Excavation diameter | 8 ft |
|---|---|
| Excavation depth | 10 ft |
| Manhole outside diameter | 5 ft |
| Manhole height | 9 ft |
| Bedding depth | 0.5 ft |
| Excavated-soil swell | 20 % |
Example results
| Bank excavation | 18.617 yd³ |
|---|---|
| Manhole displacement | 6.545 yd³ |
| Bedding volume | 0.567 yd³ |
| Backfill volume | 11.505 yd³ |
| Loose excavated spoil | 22.34 yd³ |
How the calculation works
Backfill volume = excavation volume − manhole outside displacement − bedding volume. Loose spoil = bank excavation × (1 + entered swell percentage).
FHWA FP-24 standard drawings include manholes in Section 604. Excavation, bedding and backfill geometry remains project-specific; enter the dimensions required by the plans and specifications.
FHWA Federal Lands FP-24 standard drawings — Section 604 Manholes, Inlets and Catch Basins
Scope: verify dimensions, material specifications, excavation support, compaction, reinforcement, structural or hydraulic design and local requirements independently. JobsiteMeasure estimates quantities; it does not design the installation.
Manhole Excavation & Backfill Calculator FAQs
How do I calculate backfill around a manhole?
Calculate the excavation volume, then subtract the outside volume occupied by the manhole and the bedding volume. The remaining geometric space is the backfill volume before any project-specific compaction or ordering adjustment.
What is the difference between bank excavation and loose spoil?
Bank volume is the soil volume before excavation. Loose spoil can occupy more space after excavation, so this calculator applies the swell percentage you enter separately.
Does this calculator choose a safe excavation diameter?
No. Excavation geometry, working space, sloping, shoring and protective systems must come from the project and applicable safety requirements.