While exercise bikes usually provide an effective 'distance ridden' reading that can be entered in as a manual ride, many spin bikes produce no such measurement. 

For those on a spin bike that doesn't provide a reading, you can use  the following conversion chart as a guide for recording spin classes:

DurationEffective distance
15 minutes7.5 kilometres
30 minutes15 kilometres
45 minutes22.5 kilometres
60 minutes30 kilometres