20 km, typically about 45 minutes = 27 km/h (16.5 mph). Of course, that is quite variable, depending a lot on wind direction, temperature, other cyclists (if it's a nice day, there will actually be bike traffic), what bike I'm using, and how much I'm either trying not to sweat or not caring at all.
But, the best part is that my commute is practically non-stop: from door to door, over 95% of the trip is on separated paths along a river. No traffic lights.