Detention Time Calculator
Estimate how long fluid remains in basins, clarifiers, or reactors from volume and flow data.
Detention time
72,000 s
Detention time
1,200 min
Detention time
20 hr
How to Use This Calculator
Determine basin volume
Measure or calculate the volume of the tank, lagoon, or reactor in cubic meters, liters, or gallons.
Measure flow rate
Use an average influent flow rate adjusted to the same units as selected in the calculator.
Enter values above
Provide volume and flow along with units to compute detention time in seconds, minutes, and hours.
Use detention time in design
Compare the calculated residence time with process requirements for clarification, aeration, or disinfection.
Formula
t = V / Q
t is detention time, V volume, Q volumetric flow rate. Units must be consistent; convert to cubic meters and cubic meters per second for SI output.
Example
V = 500 m3, Q = 25 m3/hr. Convert flow to m3/s (25/3600) and compute t = 500 / (25/3600) about 72000 seconds or 20 hours.
Full Description
Detention time, also called hydraulic retention time, quantifies how long a fluid element remains within a treatment unit at steady state.
The simple ratio of volume to flow guides design decisions for sedimentation basins, contact tanks, equalization basins, and other water or wastewater processes.
Frequently Asked Questions
Does short-circuiting reduce detention time?
Yes. The calculation assumes ideal mixing. Real systems may have short circuits or dead zones that lower effective residence time.
Can I use variable flow rates?
Use an average or design flow. For strongly varying flows, compute detention time for peak and minimum conditions.
How does temperature affect detention time?
Temperature does not change volume or flow directly, but process kinetics (such as biological growth) depend on temperature.
Can I convert the result to days?
Divide the hours result by 24 to obtain detention time in days.
What about batch processes?
The formula applies to continuous flow systems. For batch reactors, residence time equals the batch duration.