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Hydraulic Retention Time Calculator

Calculate how long water or wastewater remains in a tank.

Retention Time
Hydraulic Retention Time
–
hours
Tank Volume –
Flow Rate –
Retention Time –
Retention Time –
Calculation Basis

Hydraulic retention time is calculated by dividing the effective liquid volume of a tank by the flow rate through the tank.

HRT = Tank Volume ÷ Flow Rate

The result represents theoretical hydraulic retention time. Actual retention may differ because of dead zones, short-circuiting, mixing conditions, variable flow, sludge accumulation and usable tank volume. Process-specific design criteria should be used for final engineering design.