How it works
Drain minutes = (volume − retained reserve) ÷ average flow.
Input definitions
- Usable tank volume (L)
- Enter the value in the labeled unit.
- Average outlet flow (L/min)
- Enter the value in the labeled unit.
- Volume retained (L)
- Enter the value in the labeled unit.
A worked example
- Usable tank volume (L)
- 5000
- Average outlet flow (L/min)
- 40
- Volume retained (L)
- 500
Assumptions & limits
Uses only the values entered. Rates are illustrative inputs, not live quotes, legal rules or personalised advice. Check provider terms, local requirements and measurements before acting.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-19. Content checked against the stated method and examples. Our verification approach.
Report an issue with this tool or suggest an improvement ↗
Common questions
Why is this not an orifice-drain equation?
It assumes an entered average flow. Gravity outlet flow usually falls as liquid head decreases.
How does Tank drain time from average flow calculate the result?
Drain minutes = (volume − retained reserve) ÷ average flow.
What should I verify before using Tank drain time from average flow?
Uses only the values entered. Rates are illustrative inputs, not live quotes, legal rules or personalised advice. Check provider terms, local requirements and measurements before acting.