can an hour of walking at 5 m/hr burn 600 calories ??? !!!!

It sounds really far fetched to me... but the treadmill in my gym says I'm burning  600 calories / hour by just walking (fast but walking all the same)  .... is that possible... I keep adjusting my inclination ... but I dont exceed 3% .. (am fairly new to any form of exercise ... I started walking just a week ago ... prior to that I had a very sedentary lifestyle ) 

I tried changing my treadmill (went to my friend's gym) and it still shows the same value... 

are the values correct ?? am I actually burning 600 calories ??

It is hard to believe that you could still be walking at the speed  of 5 m/hr. It is more like light running speed. 3.5 is already quite brisk walking speed... And at 4.0 I find it too fast if you try to maintain full range range and correct motion.

But 60 min light run at slight inclination for an moderately overweight person, I believe, could easily burn 600Kcal.

Short answer first: They are not accurate.

Variables include your weight, age, incline, speed, overall physcial fit health, etc.  Best bet is getting your own Heart Rate Monitor.

Still, great job on walking for an hour! Keep up the great work!

Burning 600 calories in an hour of very brisk paced walking is not unreasonable for the average sized person.

 Depends on how that value is arrived at and how many stats you have to enter. If it's just push "start" and go it's probably not very accurate, if you enter your height, weight and age it's more likely to be close to the truth.

 'course, if it's been a while since it was calibrated it can be off by 20-40% even with entering stats so the odds of it being correct aren't very good.

 Never mind though - you're one workout healthier than you were before; and a little imprecision in the measurements won't be desicive over the long haul. You can enter your time in the activity calculator here on CC and have a guesstimate based on your stats that's fairly accurate if you pick the right exertion level.

 Walking is good exercise - you'll probably want to branch out into other modes of training if you have performance goals, but for overall health it's a good pick.

beyond what everyone else has said, it's giving you a "net" calories expended.  Aka, it's including the calories that you would have burned just sitting in that time as well.  So if your BMR is 2000, in one hour you'd burn 83 calories.  So only 517 of those 600 calories (if that's accurate) are "extra" calories burned.

I doubt it. I weigh 135lbs and burn appx 600 calories for a 52-55 minute run (and I run 6 miles). 

thanks a lot  for the replies... by the way I'm 5 7" tall and weight 137 pounds...   and yeah I do want to branch out to different modes but as I said earlier am very new to exercising and want to ease it slowly and don't want to rush through 

I like not wanting to rush. Crash fitness programs rarely bring any results except pain and discouragement; long-term results comes from finding out what you like to do and training for performance in that area.

 Consistency outweights efficiency when it comes to long-term effectiveness; and fun causes consistency. So I think the most important factor over the long haul is enjoying what you're doing ;)