I don’t know of a way to ‘calculate’ the movement speed. Maybe some of the unreal guys do though. Without using root motion I think this would be tricky to guess so I wouldn’t get your hopes up.
My current way is to just change the numbers in the blend space until things fit. First I’ll start by using the same full speed animation for all blend space speeds. I’ll walk around at max speed and then adjust the speed in the blend tree as needed until I figure out the max speed. From there you can adjust the other anims in the blend space up/down until they are at the correct location and things look right.
If anyone knows of a nicer way to handle this let me know!