Enter the total volume of liquid in a reservoir and the flow rate out of the reservoir into the calculator to determine the detention time.

Detention Time Formula

The following formula is used to calculate the detention time of a reservoir. 

DT = V / Q
  • Where DT is the detention time
  • V is the total volume of the tank or reservoir
  • Q is the flow rate out of the reservoir

To calculate the detention time, divide the total volume by the flow rate.

Detention Time Definition

A detention time is defined as the total amount of time it takes a given volume of water to pass through a tank or reservoir at a given flow rate.

How to calcualte detention time?

Example Problem #1:

First, determine the size of the tank. For this example, we are looking at a tank that has a volume of 500 cubic feet (ft^3).

Next, determine the flow rate out or into the tank. For this problem, the water is filling the container at a rate of 5 cubic feet per second (ft^3/s)

Finally, use the formula above to calculate the detention time:

DT = V / Q

= 500 / 5

= 100 seconds

Example Problem #2

In this next problem, we are looking at a much larger reservoir that has a total volume of 20,000 Liters (L).

The flow rate out of the reservoir is measured to be 500 liters per second (L/s)

Using the formula as we did in example 1, the detention time is calculated as:

DT = V / Q

= 20,000 / 500

= 40 seconds

detention time calculator