You pull a trout out of Montgomery Reservoir. It’s a nice fish. But how much does it weigh, and is it a keeper?

Most anglers guess. This app does the math.

Colorado Trout Weight Estimator estimates fish weight from length using standard fisheries length-weight formulas and tells you whether the fish meets Colorado’s 12-inch minimum.

• Input: fish length (slider) + species (radio button)
• Output: estimated weight, keeper verdict, length-weight curve

Weight is estimated using the formula:

\[W = a \times L^b\]

Coefficients by species (imperial, lbs/inches):

Your fish is plotted on the curve so you can see how it compares.

The app is live on shinyapps.io:

https://jbailey5280.shinyapps.io/trout_estimator/

Code is on GitHub at github.com/Saul5280/trout_estimator. No setup required.

High-altitude Colorado trout grow slower than lowland fish. A 14-inch rainbow at 10,000 feet is a different fish than one from a valley river.

Knowing the weight from length helps anglers make better decisions: keep, release, or photograph and let it go.