This is a question asked obviously by someone deciding which exercise would be better for them and coming to the best conclusion.
Methods of calculating this are different, but it seems some recent studies have come to a few conclusions. The first difference that has been found is the actual differences in calories burned from each activity. From an article published in Forbes, cycling burns 250 more calories than running per hour. This doesn't mean that people who bike do not need to worry about this because after about 2 hours the stop burning extra calories but for those looking for ways to burn more at once cycling does pack an extra punch here.
Running will also cause more localized muscle groups like your quadriceps to be used more so if you want really focused leg training you won't find it on your bike, whereas with cycling you can focus on other muscles like your glutes and shoulders.