[BD-RE slighlty smaller than BD-R?]

I had a BD job that was like 250 MB less than the maximum 25 GB size.  I tried burning it to BD-RE but ImgBurn asked if I wanted to Overburn it.  It burned to BD-R fine.  So, I'm guessing that a BD-RE's maximum available space is slightly smaller than a BD-R?  What is the maximum size then for a BD-RE?

Thanks