Calorie burn information is dramatically different between Strava IOS App and Cyclemeter IOS app. Which is more accurate? I use Cyclemeter to track rides on my iPhone 6, then when the ride is over, I send the info to Strava. When I look at the ride in Strava the calculated Calories burned for a 17 mile 90 minute ride is ~500 while Cyclemeter says ~1100 (My weight is 225lb). I do not have a heart rate or cadence monitor, so the only info being used is the GPS (distance and elevation data) and barometer(I assume) and then my weight. What factors could account for such a big difference? Do the 2 services use vastly different data from maps? Which one should I trust?
RANT - Do not read if you do not want to be offended.

A lot of calorie burn questions popping up at the moment. The problem is biometrics has become the latest fashion accessory, and everyone (manufacturers and users) are clambering on the band wagon without stopping to think what they want this data for. Manufacturers want to sell gadgets and make money, users are buying into the marketing hype. Ask yourself why do you want to know how many calories you burnt exercising? So you can justify the cream doughnut you are about to stuff in your mouth, or because you are an ultra endurance athlete struggling to main high enough calorie intake, or something in the middle? 

RANT OVER

Calorie burn can only be accurately assessed in a lab by measuring your O2 intake and output and calculating how much O2 you burnt. A very close approximation is a power meter, especially if used in conjunction with the results from a lab test. The reality is we are all born different, and just like car engines, some of us are more efficient than others, some idle less efficiently (Basal rate) and some  produce power more efficiently. To cap it off, how efficient we are depends on the food (car analogy - fuel) you put in. 

A usable, but not great approximation for calorie burn can be achieved by using a heart rate monitor, your weight and height, and the results from max heart rate test ideally including a V02Max test, and tables collated by measuring lots of people of different shapes and sizes and presuming you are average (Keeping in mind the average person is not average).  

Given this complexity exceeds the capacity of Marketing people to comprehend, they simplify it to a point its useless. If you buy a device and it claims to tell you how many calories you burnt, you can believe it - but if you continue to believe after a few minutes of research, I bet you also believe the earth is flat and man never landed on the moon. If you don't believe me, ask yourself how the above apps account for wind in their calorie burn calculation. Do they ask for you bike weight for hill climb calculations? 

However, the equipment is useful (if you are a bore at parties) - if gives you  a number you can brag about.