How accurate are calories burned using avg heart rate?

I am 139-142 lbs and 5'7", I avg approximatley 100 calories a mile at a heart rate of 143-149. There are so many variables I don't think they can be too accurate.

what comes up on your HRM?

it should be reading your HR and thus calculating calories burned based on that.

It is true, there are A LOT of variables which is why its never 100% accurate but a HRM that you program your variables into (ie: Age, Gender, Height, Weight, Body Type- ie: athlete / normal, Activity level ie: mostly sedentary, lightly / moderately / highly active etc) will give you a more true value (number of calories burned) than one that doesn't.

The more variables it asks you to program in, the more accurate it is bound to be, also do some research to find a decent brand that you can trust- My partner has a Polar, I have a Garmin- very expensive but very good.

Your cals burned are based upon your heart rate in conjunction with your other variables, but it will never be 100% unless you have a whiz bang one meant for Olympic training at Sports Institutes etc.

hrmmmm Well I have the Garmin Forerunner 405CX-

On the Garmin site the product descriptions are:

Forerunner® 305
GPS-enabled personal trainer
wireless heart rate monitor, multisport, high-sensitivity receiver, courses feature, advanced workouts, rechargeable lithium-ion battery

Forerunner® 405CX
GPS-enabled sport watch
heart rate-based calorie computation, automatic sync, wireless data sharing, high-sensitivity receiver, courses feature, advanced workouts, rechargeable lithium-ion battery.

I know on mine I have all my variables- Say if i do my 30 min Yoga Buns DVD- I will burn between 170-230 calories each time. I just have it set to the "running" setting, and don't bother with the GPS for that one, GPS is only useful for logging where you went on your computer and the distance etc, doesn't have a lot to do with calories at all.

I am not sure why its not saying you are burning much.

how heavy and tall are you? Last night my partner and I went for a ride, he burned 600 cals and I only burned 254! He only did about an extra 3km more than me- so maybe an extra 5 minutes worth but burned double what I did in total. Basically the bigger you are (both in height and weight) the harder your body has to work to do the same thing, thus the extra calories burned. also the more you lose weight and get fitter, the lighter and fitter you are which means that the easier exercises won't burn as much as they used to or as much as your harder exercises do now.

Or maybe you are right, maybe it isn't reading it accurately, maybe try just setting it to the running setting, that's what I do and I think it reads/ works accurately.

ps: I have never done it and don't know what it is even though SO many people on MFP talk about it, What exactly does p90x entail?

I have the Garmin 305, too, and am having the same issues. I did P90X- Core Synergistics this morning and it said I burned 38 calories! Haha! So I calculated my calorie burn using my average heart rate and this online calculator:

http://www.braydenwm.com/calburn.htm

I'm 5'5", 135 lbs, 33 yrs old and my average heart rate was 112. It says I burned 350 calories and that was about what I expected. I'd say it's close enough.

Ditto!!! I have the Garmin 305 and it say 23 calories on plyo for me I use the same website listed here at braydenwm and it seems to be accurate. I compared it to my Garmin when I ran and my calories did calculate, and they were within 5 calories based on Average heart rate.