Spoke size ?

Hello people i am new to the site and searching for what size spoke i may need for my E-bike. I have a 29" but not sure what size spoke to get. I have searched and read that i need a 259 mm but not sure if that's correct. I seen a post on this site about a guy having same question / issue back in 2013, but never really resolved. This is my 3rd E-bike so i have laced lots of wheels with 24" , 26" but not a 29er yet. I tried the online calculator but that's not much help.

You need rim ERD (effective rim diameter) motor flange diameter and to lesser extent flange width to make use of calculators.

Maybe if you tell us what motor and rim you have, somebody might be able to help.