From everything, I've read this is about right, emphasizing the word "rough". By the same token, I use 100 per mile as a rough estimate for walking or running. You really need to use per mile (or km) estimates, not per hour, since that accounts for the difference in intensity while per hour does not; e.g. if you use 30 per mile and go 10 miles, that will be 300 calories, but it will take half as long if you go 20 mph as opposed to 10 mph, so the per hour is much different depending on speed, while the per mile is not.