Hello!
In general you can always try the wikipedia article for a route, many articles include the distances between stations. Other than that, you can also use a navigation application like Google Maps and find out the distances between two adjacent stations by entering one as start and the other as destination and looking at the walking distance. This is not completely realistic though.
If you could tell me, which routes you're looking at, or at least the country, I may be able to help you further.
Regards
Taurus Fan