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Manhole / Utility Concrete Collar Calculator
Calculate the concrete in an annular utility collar from the outside diameter, clear opening and thickness shown on the project detail.
Calculate manhole / utility concrete collar quantities
Use this calculator for a circular concrete collar when both the outside diameter and clear opening are known. It subtracts the inner cylinder from the outer cylinder, multiplies by the number of identical collars and applies the allowance you enter.
Formula: Net collar concrete = π × [(outer diameter ÷ 2)² − (opening diameter ÷ 2)²] × thickness × collar count.
Useful for manhole concrete collar volume, valve-box collar concrete, utility collar cubic yards and annular concrete 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
Use project-specified geometry and material requirements. Allowance is shown explicitly rather than hidden inside the dimensions.
Worked example
The example uses the calculator's starting dimensions so the arithmetic can be checked independently.
Example inputs
| Identical collars | 4 count |
|---|---|
| Collar outside diameter | 6 ft |
| Clear opening diameter | 3 ft |
| Collar thickness | 0.67 ft |
| Concrete allowance | 5 % |
Example results
| Concrete to order | 2.21 yd³ |
|---|---|
| Net geometric concrete | 2.105 yd³ |
| Gross outer cylinder | 2.806 yd³ |
| Opening deduction | 0.702 yd³ |
How the calculation works
Net collar concrete = π × [(outer diameter ÷ 2)² − (opening diameter ÷ 2)²] × thickness × collar count.
FHWA Federal Lands standard drawings include manholes, inlets and catch basins in Section 604. Collar geometry, reinforcement, frame adjustment and pavement details are project-specific; this calculator only converts supplied annular geometry into concrete quantity.
FHWA Federal Lands FP-24 standard drawings — Section 604
Scope: verify dimensions, material specifications, structural/electrical requirements, reinforcement, excavation support and local requirements independently. JobsiteMeasure estimates quantities; it does not design the installation.
Manhole / Utility Concrete Collar Calculator FAQs
How do I calculate concrete for a manhole collar?
Calculate the outer circular slab volume, subtract the clear opening through the middle and multiply by the number of identical collars.
Can I use this for valve boxes or other utility collars?
Yes, when the collar is circular and can be represented by a known outside diameter, opening diameter and thickness.
Does this calculator determine collar dimensions or reinforcement?
No. Use the approved project detail for geometry, reinforcement and pavement/interface requirements.