Calorie burn seems very high per mile of walking

[Rara]

Hello, 

I have been using my Garmin Forerunner HR monitor to track my calories burned on walks & runs. Now that I have started using my fitbit force, I notice that the calorie burn is way higher for walking and somewhat higher for running. 

Example: 
I took my dog for a walk today and my Garmin read 1.67 miles (which I trust) & 125 calories burned. My fitbit says 1.55 miles (a little off, but I'm not real concerned with that) and 218 calories burned. To get this number, I subtracted my cals burned before walking from those I had after. 218 calories for just 1.67 miles seems like a lot! That is almost twice what my garmin calculated. I have read multiple times on running-related websites (see link below) that walking doesn't even burn 100 cals per mile (more like 70-80) so this was very surprising for me. 

Another Example: 
Went for a 3.27 mile run & burned 346 calories (Garmin), yet my fitbit showed 3.14 miles & 382 calories. Not quite as big of a difference as calories burned walking, but still more. 

According to this website: runnersworld.com and the formulas below, my TOTAL calories burned per mile (including BMR) would be about 69 calories, without BMR it would be 39 calories per mile. It seems Fitbit's estimation is around 125 calories, which is twice what this gives me. These are the formulas shown on the website, which I have found pretty consistent with other devices (like Runkeeper), not just my Garmin.

Activity          Your Total Calorie Burn/Mile          Your Net Calorie Burn/Mile 

Running.       .75 x your weight (in lbs.).            .63 x your weight 

Walking.          .53 x your weight.                       .30 x your weight

I have been losing weight with just my Garmin & MFP, so I am scared that by following the fitbit calories burned that I will gain weight, since it usually adds several hundred additional calories per day. I have my height & weight entered correctly in Garmin & fitbit. 

Any input would be greatly appreciated! I would hate to think that I can't trust my fitbit 😞 I would love if there was some great explanation for why I AM burning that many calories 🙂 I weigh 130 lbs, if that helps at all. 

[Kapalua]

Using a Garmin GPS watch and HR monitor, your readout of calories burned is going to be more accurate from the GPS watch. Caloric expenditure data interpreted by a more sophisticated HR monitoring device is more reliable than a device without HR monitoring. 

That said, fitbit is pretty good at what it does. Just not as accurate as an expeensive and sophisticated dedicated runner's watch with HR monitoring or even a much less feature filled HR monitor that is able to also access movement types to calculate caloric burn algorithms.

[Rara]

Thanks for your reply! Is there any way I can make it more accurate? It seems my stride length is about right (sometimes over, sometimes under).  If I take my dog for a 15 minute walk, it seems that it registers most of those 15 minutes as "Very Active" minutes, which they are not! We usually walk at an 18-20 minutes/mile pace. I would like to be able to wear it all day, as well as while walking & running, and be able to trust the numbers. If it is doubling my calories, it is very inaccurate and not worth the great reviews regarding accuracy that it has received.

[Rara]

I have also been wondering if maybe the dramatic increase in calories is because fitbit is trying to account for "after burn" calories, or the calories that your body burns after an activity is complete but before it completely recovers back to its BMR. Hmmmmm...

After burn explained here: http://www.runnersworld.com/weight-loss/running-v-walking-how-many-calories-will-you-burn

[Rara]

I think I have figured out the real issue. After reading through the forums, it seems that many people are getting "very active minutes" for doing things that aren't very active, like a slow-paced walk. Not only is fitbit counting these slow walks as very active, it is giving them calories as if they were very active.I don't think it's anything we have control over, but a bug with fitbit. I hope they get this figured out soon! I'm about ready to go return this thing...