Go to freedieting.com and on the left you'll see some 'calculators'. Click on the "calories burned" and you can look up how many calories you burn doing various activities based on your current weight and how long you do that activity (how many minutes).
Jumping rope is great cardio, but it's hard on the joints and back (high impact). Bicycling is easier on the body, but you've got to push hard or put it in a gear with a lot of resistance to get a good calorie burn and not just coast along.