Crappie weight and length rule
Here is a nice tool for estimating weight of crappiei by measuring them. This is no replacement for putting the crappie on the scales but it is a quick way to estimate weight. Of course if the crappie is in poor condition post spawn or fat with eggs the weights will vary but this is a very good rule of thumb.
I printed and laminated and stuck it to the inside cover of one of the compartments in my boat for reference while on the water.