Calculate detention time, flow rate, or volume from two inputs in gallons, liters, cubic meters, or cubic feet and return results in minutes, hours, or seconds.
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Detention Time Formula
The detention time calculator uses the relationship between volume, flow rate, and time. In its base calculation, volume is in gallons, flow rate is in gallons per minute, and detention time is in minutes.
- DT = detention time
- V = tank, basin, or vessel volume
- Q = flow rate through the tank, basin, or vessel
If you are solving for volume, the formula is rearranged as:
If you are solving for flow rate, the formula is rearranged as:
The calculator can solve for any one missing value when you enter the other two:
- To calculate detention time: enter volume and flow rate. The calculator divides volume by flow rate.
- To calculate volume: enter flow rate and detention time. The calculator multiplies flow rate by detention time.
- To calculate flow rate: enter volume and detention time. The calculator divides volume by detention time.
When different units are selected, the calculator first converts the inputs to gallons, gallons per minute, and minutes, performs the calculation, then converts the result back to the selected output unit.
Common Unit Conversions for Detention Time Calculations
| Measurement | Unit | Equivalent Used in Base Calculation |
|---|---|---|
| Volume | 1 liter | 0.264172 gallons |
| Volume | 1 cubic meter | 264.172 gallons |
| Volume | 1 cubic foot | 7.48052 gallons |
| Flow rate | 1 liter per minute | 0.264172 gallons per minute |
| Flow rate | 1 cubic meter per hour | 4.40288 gallons per minute |
| Time | 1 hour | 60 minutes |
Typical Detention Time Interpretations
| Result | What It Means |
|---|---|
| Short detention time | Fluid passes through the tank quickly. This may reduce contact, settling, or reaction time. |
| Long detention time | Fluid remains in the tank longer. This may improve contact time, settling, or treatment, depending on the process. |
| Zero or near-zero flow | The formula becomes invalid or produces an extremely large detention time. Use the actual operating flow rate. |
Example Detention Time Calculations
Example 1: Calculate detention time
You have a 5,000 gallon tank and a flow rate of 250 gallons per minute.
The detention time is 20 minutes.
Example 2: Calculate required volume
You need a detention time of 45 minutes at a flow rate of 80 gallons per minute.
The required volume is 3,600 gallons.
FAQ
What is detention time?
Detention time is the estimated amount of time water or another fluid remains inside a tank, basin, or vessel. It is calculated by dividing the volume by the flow rate. For example, if a tank holds 1,000 gallons and the flow rate is 100 gallons per minute, the detention time is 10 minutes.
Is detention time the same as contact time?
They are related, but not always identical. Detention time is a simple hydraulic estimate based on volume and flow. Contact time may account for actual mixing, short-circuiting, baffling, or process-specific efficiency. In practical treatment systems, the effective contact time can be less than the theoretical detention time.
Why does the calculator require exactly two values?
The formula has three variables: volume, flow rate, and detention time. If you enter any two, the third can be calculated. If you enter only one value, there is not enough information. If you enter all three, there is no missing value to solve for.
