Measureing calories burned while swimming?

Well, I'll speak for a friend of mine (making this 2ndhand info, but hey...)

I know that there is at least ONE hrm that does work underwater, coz he's really wanting to get it. It also counts laps for you somehow. Craziness.

But I would imagine that by far the most common answer you're gonna get is from off-the-cuff estimates, calorie charts along the lines of "If you weigh THIS much and swim at THIS level for THIS amount of time, then..."

I know that for most of my (admittedly non-swimming) activities, I just blindly take the number MFP estimates for me. I'm getting more of an idea what my body really burns as time goes on, but for most stuff I let the computer do it.

The device she's talking about isnt a HRM, it's called a pool mate (google it) there's a pro version and a standard... it's really a swim performance monitor, but it does count calories burnt, but again this is only an estimate!, the pro one is great if your trying to swim train aswell as you can upload your swim data to your PC.

You shouldnt be too concerned about the high calories burnt during swimming or that MFP gives, or the pace, as long as your heartrate is in the 'fat burn' zone than you'll be doing exactly that (i.e calories) and the high levels of burn are backed up by reasearch by harvard medical school which estimates someone of 185 lbs will burn 444 calories per half an hour of breastroke, of course it's more for a larger person (see link... http://www.health.harvard.edu/newsweek/Calories-burned-in-30-minutes-of-leisure-and-routine-activities.htm)

The best stroke for high calorie burn is breaststroke, it's the most inefficent stroke and therfore uses the most energy. I personally swim 65-70minutes solid, and record 60 to account for slow downs or any short stops, my pace is generally about 2.5-3km per hour (30-40 seconds per lenght in a 25m pool) and i weigh 206lbs... this all in burns 938 for the hour!

I hope that helps!