Correct alternator/fan belt size?

[mrfatboy]

I will be changing my belts soon and that pelican parts and autohauzaz only sell 10mmx900mm replacement belts.

I currently have a 10mm x 925mm belt. Searching the forum yielded this post which also suggests that 10x925 is correct for an early 68/69 280sl.

https://www.sl113.org/forums/index.php?topic=3713.0

Will a 10mm x 900mm work?  What should be the correct size?