Operator calculator
Detention Time calculator
Divide basin volume by flow to find how long water stays in the tank.
Calculator
Detention time
300 min
- 1. 150,000 gal ÷ 500 gpm = 300 min
- 2. 300 min ÷ 60 = 5 hr
For instructional use. Results assume the standard conversion factors shown on this page. Actual field calculations may need chemical strength, density, temperature, and other adjustments, so check your plant’s procedures.
Formula and inputs
detention time (min) = volume (gal) ÷ flow (gpm)
| Input | Unit |
|---|---|
| Volume | gal |
| Flow | gpm |
| Result: Detention time | min |
Conversion factors used: 60 minutes per hour.
When to use it
Detention time tells you how long water is held in a basin, clearwell, or tank. It affects settling, disinfection, and how quickly a change reaches the effluent.
Volume and flow must use the same time base. This version uses gallons and gallons per minute, so the answer comes out in minutes.
Applies to: Water Treatment, Water Distribution, Wastewater Treatment, Collection Systems.
Exam tip: Check the question's units first. If flow is in MGD, convert volume and flow to the same basis.
Study guides
Build the math skill behind the calculator
Water Operator Math Made Simple walks through the formulas step by step.
Water Operator Math Made Simple
A Step-by-Step Guide to the Math Every Water Operator Needs to Know