Sitework quantity calculator
Catch Basin Excavation & Backfill Calculator
Calculate the excavation and backfill around a catch basin without counting the structure itself as fill. Enter the pit, structure and bedding dimensions from the project.
Calculate catch basin excavation & backfill quantities
This catch basin excavation calculator finds the pit volume, subtracts the outside volume occupied by the catch basin and the bedding layer, then reports the remaining backfill and loose spoil.
Formula: Backfill volume = excavation length × width × depth − catch-basin outside volume − bedding volume. Loose spoil applies the swell percentage you enter to bank excavation.
Use it for catch basin excavation volume, catch basin backfill quantity, inlet-box earthwork and catch basin spoil estimates.
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 length | 8 ft |
|---|---|
| Excavation width | 8 ft |
| Excavation depth | 8 ft |
| Catch basin outside length | 4 ft |
| Catch basin outside width | 4 ft |
| Catch basin height | 7 ft |
| Bedding depth | 0.5 ft |
| Excavated-soil swell | 20 % |
Example results
| Bank excavation | 18.963 yd³ |
|---|---|
| Structure displacement | 4.148 yd³ |
| Bedding volume | 1.185 yd³ |
| Backfill volume | 13.63 yd³ |
| Loose excavated spoil | 22.756 yd³ |
How the calculation works
Backfill volume = excavation length × width × depth − catch-basin outside volume − bedding volume. Loose spoil applies the swell percentage you enter to bank excavation.
FHWA FP-24 standard drawings include catch basins, inlets and manholes in Section 604. Use excavation, bedding and structure dimensions required by your 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.
Catch Basin Excavation & Backfill Calculator FAQs
How do I calculate backfill around a catch basin?
Calculate the excavation volume, subtract the catch basin outside volume and bedding volume, and use the remaining space as the geometric backfill quantity.
Is this a catch basin sizing calculator?
No. It does not size the grate, outlet pipe or drainage capacity. It estimates installation earthwork after the catch basin and excavation dimensions are known.
Why is structure displacement deducted?
The installed catch basin occupies part of the excavation, so that volume cannot also be counted as backfill.