how many calories do u burn if u walk a mile

Well, what was the terrain like (was it all flat / asphalt, were their hills, stuff like that) and how fast were you going / how long did that mile take for you to complete? Just a mile isn't enough info to know how much you burned.

Also, if you go to "exercise" in the top menu, you can log your exercise and it'll give you a good estimate of the calories burned.

I walked three miles at 4 MPH this morning = 396 cals

everyone will be different based on their age, height, weight, sex and fitness level

Age, sex, fitness level and speed make virtually no difference. All that really matters is distance and body weight.

I'm going to have to seriously disagree with this....fitness level can make a huge difference. A fit person has a much more efficient system and will be able to do the same work with clearly less energy expenditure than an un-fit one.

Nope. Walking 3 miles takes about the same amount of energy regardless of fitness level. What an improved fitness level gives you is the ability to do more, in less. IE, it allows you to generate higher levels of power, over longer periods of time.

But power is not the same thing as work, and confusing the two is a large contributor to people's misunderstandings on this issue. For doing X, it's the same actual energy expenditure, either way.

Look at 2 150lb people doing the same distance, one hits the end barely winded and the other is flushed, breathing hard, and sweating. If you just look at the fact that one person is putting off a heck of a lot more heat, the by product of all the biological processes involved, and one person is working like hell to shed heat, that person is doing a lot more work.

Again, no, that is not correct. A fit person's body has physiological advantages that allow less stress for the same amount of energy expenditure. IE, they can maintain a higher power output for the same level of physical stress. *That* is consistent with what you describe above.

But for the same distance, using the same biomechanical motion, there is negligible difference in the actual energy expenditure itself.

Power != Work.

Speed doesn't matter!?! Maybe not between a 3 and 4 mph walk for most basically fit people, but even a 2-3 MPH difference can add up to a big difference at the end.

A 3 MPH difference from a 3MPH baseline is either 0 (i.e. not walking at all) or 6 MPH (i.e., running).

I really think you need think through your examples a bit better.

But you aren't taking recovery period into consideration either, which is something that I think a lot of people miss out on. The closer you work to your relative maximum intensity level, the greater the impact on the recovery period. IE, the run that leaves one person face-down on the track and the other slightly winded are going to have a significantly different net effect within the next 24-48 hours.

This is the entire reason that High Intensity Interval Training is as effective as it does, since it pushes the person very close to their relative intensity maximum, which makes for a significantly increased calorie burn in the same time and/or distance.

I can jog a 5k without a whole lot of trouble, but for other people that will require a very significant output, and in the end that workout will cause 2 significantly different burns.

Net calorie burn per mile , running: .63 x body weight
Net calorie burn per mile, walking (less than 5 mph?): .3 x body weight

Calorie burn from Huffing and puffing, hacking cough , wheezing, curling up in the fetal position on the side of the road not included. These are all things I plan on doing should I for the first time attempt a 2 mile run I mapped out some weeks back.