Distinguish geometric tank headroom from permitted working capacity.
What does spare volume after a proposed addition actually mean?
Use the matching calculator
Use this decision sequence
- Use inside cylindrical dimensions only when the vessel is a straight vertical cylinder.
- Enter current liquid volume and proposed addition on the same volume basis.
- Compare their sum with geometric capacity and report any exceedance separately.
- Use the applicable manufacturer working capacity outside this pure geometry model.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Geometric capacity | Inside area times cylindrical height. |
| Permitted working capacity | An external product specification. |
| Freeboard height | The geometry above the proposed liquid level, not an automatic operational allowance. |
Worked comparison
A cylinder with 2 m inside diameter and 2 m height has capacity 2π m³. If it already holds π m³ and another π m³ is proposed, geometric spare volume is zero. That does not mean the vessel is permitted to operate at its exact geometric top; actual working limits and internal displacement must be checked separately.
Check before using the estimate
No pressure, overfill protection, drinking-water suitability or operating fill limit is selected.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.