River Difficulty Rating Calculator

Estimate whitewater class (I-VI) from river gradient, flow rate, channel width, obstacle density, and water temperature.

Inputs

Gradient (ft/mile)

Flow rate (cfs)

Channel width (ft)

Obstacle Density

Water temperature (°F)

Tab to move between fields

Results

Whitewater class (I-VI)

Difficulty score (0-100)45.6

Gradient contribution16

Flow per ft width (cfs/ft)16

Cold water risk score5.5

Suggested experience (years)5

Class LabelIV — Advanced

How to Use This Calculator

Look up the river gradient (ft per mile) from topo maps or guidebooks — Class II is ~10 ft/mile, Class IV is ~40–60 ft/mile.
Check a USGS gauge for current flow rate in cfs and enter it.
Enter the average navigable channel width in feet.
Select obstacle density from few/none through very dense based on your scouting or guidebook description.
Enter the water temperature in °F — cold water raises the consequence rating and overall difficulty.
Read Whitewater Class (I–VI) and Suggested Experience (years) to match the run to your skill level.

What each input means

Gradient (ft/mile): Riverbed drop per mile. Class II ~10, Class III ~20-30, Class IV ~40-60.
Flow rate (cfs): River discharge in cubic feet per second from USGS gauges.
Channel width (ft): Average width of the navigable channel.
Obstacle Density: Density of rocks, strainers, and other obstacles.
Water temperature (°F): Colder water increases consequence rating and overall difficulty.

What each result means

Whitewater class (I-VI): International Scale of River Difficulty rating.
Difficulty score (0-100): Composite difficulty score from all factors.
Gradient contribution: Points from riverbed slope (0-30).
Flow per ft width (cfs/ft): Flow concentration — indicates hydraulic power.
Cold water risk score: Additional difficulty from cold water consequence (0-20).
Suggested experience (years): Minimum recommended paddling experience for this difficulty.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Gradient (ft/mile) = 20, Flow rate (cfs) = 800, Channel width (ft) = 50, Obstacle Density = 2 = 5 input(s) provided
Calculate Whitewater class
Whitewater class
4 = 4
Calculate Difficulty score
Difficulty score = gradientScore + flowScore + obstacleScore + coldScore
45.6 = 45.6
Calculate Gradient contribution
Gradient contribution
16 = 16

Engine last updated July 28, 2026. Checked against 3 independently-derived tests — how we verify calculators.

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