# Big difference between Zwift caliories and Wahoo HRM

Hello All. I know it’s always just an estimate but Wahoo says I burned 720 calories and Zwift reported 320. What can account for this wide difference? This was a 1 hour sub 2 ride, I’m 48 kg and typically ride 2.1-2.2 so stay with the group. I’m curious about the calculations.

320 sounds about right, 720 is way too much for a 1 hour easy ride

I thought that. Thanks. I wonder how Wahoo measures

An approximation for calories burned by a typical person is:

Average Power x 3.6 x hours cycled

which in your case would be approx 100W x 3.6 x 1.0 = 360 kcal. We know the work done in joules and the calculation simply assumes a physiological efficiency of something like 24%, but most people are within a few % of that. So the Zwift figure is clearly much closer. If Wahoo is using HR to estimate power/work done it will have no idea of the work actually done or power you were putting out - HR depends more on aerobic fitness and not raw power so it will usually be way off! And that’s before we consider HR lag.

Thanks so much. That is super helpful. I knew the high number was unrealistic but didn’t understand the formula