Here is a link to an online relative weight (RW) calculator from Alabma and Auborn Extension for a few common pond fish species including crappie. Know the length of the fish and its weight and it will calculate the Relative Weight. Note that RW does change during the year for fish species depending on food sources, spawning condition, and water temperature. Note there are some measurable differences in standard weights between black and white crappie.
https://www.aces.edu/blog/topics/fisheries/fish-relative-weight-calculator/

See the info in this link to the standard weights of numerous fish species - FYI the very useful PBoss post was created by PB member D.Nicholaus
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Main=29038&Number=372789#Post372789