Math/logging assistance: I can't brain today.

ElizabethKalmbach

OK, so my Fitbit Alta is dumb and freezes and hangs halfway through my 3.87 mile walk home from work about twice a week. When this happens, because the distance is static, I can log the walk manually if I notice that the hardware is stupid.

When I log a 3.87 mile walk that took 68 minutes at 3.5 mph, I get 377 calories burned.
My Fitbit normally gives me 7400 to 7700 steps and 475-490 calories for the effort - there's no heart rate monitor on it, so it's somehow calculating this based on step count.
If I manually log the walk into my Fitbit, it logs it as 6100 steps and gives me 252 calories...

Which value is (most) correct? I only have about 2 weeks of data to work with since I got the new Fitbit, and I *am* losing weight, but since I am on exercise restriction (to reduce inflammation - which I have translated as no lifting) and retaining a crapload of water (I've lost 10 lbs in about 2 weeks - see also exercise restriction), I'm kind of unsure which amount of exercise calories to eat back and which value is most likely to be accurate, since the number I normally eat back is about twice as high as the number a manual entry generates. For eating purposes, I can split the difference but for math and comprehension purposes I am somewhat frustrated.

I'm not *that* worried about the eating, but since I do use the hardware trackers to troubleshoot medical issues with my doctor, I want to understand how they're getting their numbers and interacting with each other vs my activity level and why the numbers are so different. What am I messing up?

lorrpb

I don’t know your stats, but a 150 lb person burns about 50 cal per mile or 193 cals for 3.87 mi. Prorate based on your weight. This is based on a standard formula for walking calories, the details of which escape me at the moment.

middlehaitch

The formula @lorrpb is referring to is 1/3weight x distance in miles = cals burnt.

Cheers, h.

ElizabethKalmbach

Oh, wait. Stride length and step count versus actual Google Map mileage.

My stride on a treadmill with no incline is 39".

If I reverse math the step count to the Google map mileage, outside, on a sidewalk with various inclines and streets to cross, my stride length looks like 32" on average.

If I change my stride length to 32 from 39, the mileage matches, and when the mileage matches the step count matches and rate of speed calculations should match up better too. ... BUT, changing stride length doesn't appear to change the Fitbit calorie calculation for a manual input walk versus a step counted walk. I *do* feel confident adding numbers with MFP calculations for the walk, but I still have no idea how Fitbit is coming to it's calculated conclusion.