We use something called the relative weight formula, a method commonly applied in fisheries science.   This formula predicts the length and weight of a fish by using species-specific constants that reflect its natural shape and growth patterns.

For example, the formula generally takes the form:

Weight = a × (Length)^b

Here, a and b are species-specific coefficients, which vary depending on the fish’s body type. By plugging in the length of a fish, we can estimate its weight—or vice versa—with impressive accuracy.

To ensure realistic estimates, we apply the relative weight concept, where a relative weight of 0.9 is considered the average or healthy benchmark for most species. This means that if a fish’s weight closely matches what is predicted at 0.9 relative weight, it’s in good condition, so that's the estimate we provide.

However, the system has its limits. Any fish with a relative weight below 0.25 or above 2.5 is flagged as an error because these values fall outside the realistic biological range. Extremely low or high relative weights indicate a miscalculation or unrealistic input. By staying within these boundaries, we provide you with reliable and meaningful estimates for your catches.

Here's an example of a weight vs length curve for Tiger Musky. 

Image Credit: EDSClikes2hunt - Own work, Public Domain, Wikimedia Commons