Welcome to the SeeMeCNC Community

I'm in need of the correct "calculations" for determining arm length's versus frame height..

My current height between the print bed and the top of my rail is 25".

I read some where that arm length is equal to half the vertical rail height?! Is that correct? and if so is it the length from where the center of the u joints at the carriage to the center of where the hot end will be positioned? or just center to center of each joint at the end of each rod?

I guess I'm a little confused about how you guys/gals figure the lengths of the rods vs. height of towers and build area..

Anyhow, thank you ahead of time for any clarification someone can provide.

As long as the arms can reach across the entire bed, you're fine. The height isn't dependent on that measurement. Both measurements can be accounted for in the firmware and don't necessarily need to be directly "related" to each other.

There are ranges of arm length that will and will not work, but they're related to print area. Unless you're using non-standard parts/configuration on your machine, you can make the aluminum extrusions as long as you can find a timing belt for.