FWIW, the stationary bike at the gym registers about 36 cal/mile at load
#11 out of 25. My cadence is 105-110, but the calories appear to be distance, not speed, related.
My Cannondale CX on rollers at home seems a greater workout, based on heart rate and sweat production (even with a cooler room and closer fan than at the gym). Cadence at home is 90-100.