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 reservior
- Q is the flow rate out of the reservoir

## 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