I have a friend who has an exercise bike with no mileage calculator. What would you think would be the average distance rode in 10 minutes for a beginner? I've googled a few things and come up empty (guess I'm not thinking like a search engine this morning, lol). The only thing I can think of is for her to ride her real bike a known distance and see how long it takes.
10 minutes is a easy comfortable mile for a stationary bike, especially if she's not pushing herself that hard. It's more difficult in real life with pavement conditions, wind resistance, weather, and constant focus on biking technique, so she might not make the mile. But on the bike, yeah, she might even be surpassing that distance.
A cheap method to figure it out --- use a pedometer to figure out how many leg strokes she did in a mile on a real bike outside (no coasting), then transfer to the same number on her stationary bike. The only difference is that sometimes the stationary bike has smaller crank length than a real bike.
hth