Enter the flow path length, and the flow path slope into the calculator to determine the time of concentration on a small basin (1-112 acres).

Time of Concentration Formula

The following equation is one of many different equations for calculating the time of concentration.

Tc = (.0078 * Lc) ^ {.77} / Sc ^ {.385}
  • Where Tc is the time of concentration
  • Lc is the flow path length
  • Sc is the flow path slope

Time of Concentration Definition

A time of concentration is defined as the time it takes runoff water to travel from the hydraulically most distant point in the watershed to the outlet of the watershed.

Time of Concentration Example

How to calculate time of concentration?

  1. First, determine the flow path length.

    Measure or calculate the total flow path length or length of the channel.

  2. Next, determine the flow path slope.

    Measure or calculate the slope of the flow path or channel.

  3. Finally, calculate the time of concentration.

    Calculate the time of concentration using the equation above.


What is time of concentration?

The time of concentration is the time it takes water runoff to flow to an outlet. There are many equations to calculate this because there are many different geographies of runoff. The equation above should only be used for simple channels and small basins.

time of concentration calculator
time of concentration formula