Froude Number Calculator
Enter flow velocity and hydraulic depth to compute the Froude number and instantly classify the flow regime.
Flow Parameters
Average velocity across the channel cross-section
For rectangular channels: water depth. In general: A / T (area / top width)
Flow Regime Reference
Fr < 1
Subcritical
tranquil / slow
Fr = 1
Critical
minimum energy
Fr > 1
Supercritical
rapid / shooting
Enter velocity and depth, then click Calculate
Froude Number
—
—
Formula Breakdown
Fr = V / √(g · D)
Velocity (V)
—
Hydraulic Depth (D)
—
Gravity (g)
—
Wave Celerity √(g·D)
—
Note: At Fr > 1, a hydraulic jump may form if downstream conditions create a lower-energy subcritical state.
Copied!
Summary
Enter flow velocity and hydraulic depth to compute the Froude number and instantly classify the flow regime.
How it works
- Enter the mean flow velocity in the channel (m/s or ft/s).
- Enter the hydraulic depth — cross-sectional area divided by top width (m or ft).
- Select your unit system (SI or Imperial).
- The calculator applies Fr = V / √(g · D) and displays the result.
- A color-coded badge shows the flow regime: subcritical (Fr < 1), critical (Fr = 1), or supercritical (Fr > 1).
Use cases
- Classify open-channel flow for hydraulic engineering design.
- Check whether a river or spillway section operates below or above critical depth.
- Determine the likelihood of a hydraulic jump forming downstream.
- Validate physical model similarity in Froude-scaled laboratory flume tests.
- Support dam and weir overflow analysis.
- Solve undergraduate fluid mechanics and hydraulics coursework problems.
Frequently Asked Questions
Last updated: 2026-07-23 ·
Reviewed by Nham Vu