Hi, I can't help you exactly, but I have a 24" Finnex Ray II DS. Without the "feet" attached to each end, it measures 23.75". With the feet, but without the screws that clamp onto the side of the tank, it measures 24.25". With the screws, it's ~24.75".
The cord (when folded flat against it) adds about 1/8" more, but does not add any length when the "feet" or screws are on (sits flush with those).