All calculations are estimates, but I've found SP's to be pretty accurate. When I use my heart rate monitor, it's generally within 20 calories of SP's estimates. Running/walking are fairly well studied, so the relationships between size, speed, and heart rate are fairly reliable.
I can't comment on this specific website, since I haven't used it, not without knowing the full data of the people reporting these estimates. What kind of estimates are we talking about?
In the end, it's all an estimate, and as long as they're not reporting something absurd (like 2-300 calories per mile) it's probably not that off. Are they heavier than you? The more you weigh, the more you will burn. Someone that weighs 230 will burn a lot more calories than someone who weighs 130.
I did do a google search for "runtastic calorie accuracy" and there were a few complaints at the top about it being inaccurate.
Here's the top ones I found: my.support.runtastic.com/runtastic/topics/
Edited by: DRAGONCHILDE at: 4/13/2013 (09:33)