I was curious if anyone has compared the accuracy of the calorie counting function on say a Garmin Forunner 305 to a power meter, such as a Powertap? I assume a power meter would be more accurate, I was just wondering if my Garmin is way off or not?

My understanding is that the Garmin calorie counter does not use the available HR and altitude data, making it practically useless.

I was curious if anyone has compared the accuracy of the calorie counting function on say a Garmin Forunner 305 to a power meter, such as a Powertap? I assume a power meter would be more accurate, I was just wondering if my Garmin is way off or not?

There's a thread about this in the Road Biking forum. It's titled 5000 Calories or something along those lines.

Bottom line is that the Garmin's are WILDLY innaccurate. 40cal/mi of riding seems to be what some people use for estimations.

PowerTap figures are given in that thread as well. It's a recent thread.

I use the online calculators that go by 10-12mph, 12-14, 14-16 and 16-18mph. They at least allow me to compare rides accurately. I know that my usual 100 minute 30+ mile night route burns 1700 or so calories according to the websites. At the 40cal/mi estimation it puts it more like 1200 calories!

Time to cut out those Big Macs I thought I was earning!

I know that my usual 100 minute 30+ mile night route burns 1700 or so calories according to the websites. At the 40cal/mi estimation it puts it more like 1200 calories!

Time to cut out those Big Macs I thought I was earning!

I think you might have your numbers backwards? If you found out that you are burning 1700 instead of the 1200 you thought you were, then you could afford a big mac. STILL, that's no reason to eat a big mac! They are nasty and just plain bad for ya ;)

I'll look for that thread that you talked about. I pretty much planned on them being inaccurate but at least they give me a trend to follow. I know some have mentioned that they don't take into account your heart rate. At first I thought that might be necessary to know for true calorie burned calculations but now I don't think it matters at all. My reasoning is this: As we exercise more and more, our heart rates should decrease for a given amount of work. An example, when I first started running and biking my HR would easily be in the 190s to climb a certain hill by my house. Now that I have lost 13 pounds and I'm in better shape, I did the same hill today at my fastest pace yet and my HR was in the 170s.

Not to turn this into a training discussion on the electronics forum (maybe one can see now just how interrelated the different facets of biking are) but I just had to chie in to the HR comment made earlier. Thanks for all the responses thus far.

I would think you could make a GPS version that was reasonably accurate. The main thing you couldn't account for that way would be wind. But calories in don't necessarily equate to calories out, so I"m not sure what the point of the whole thing is either way.

But calories in don't necessarily equate to calories out, so I"m not sure what the point of the whole thing is either way.

I'm not sure I know what you mean there.

Calorie count on ANY device is useless at any rate.