Hi eceryone, am I alone in wondering why Zwift displays the number of KJ used during a workout and displays it as Kcal, or am I wrong?
For example on my latest workout, I averaged 233W for 1h16’
You’ll see that Zwift says I burnt 1026 Kcal, whereas it should be 1026 KJ.
233 W are 233 J/s time 4560s = 1062 KJ which make about 255Kcal
Correct me if I’m wrong, but I think that’s a bug!
They’re assuming that meat engines (ie you and me!) are about 25% efficient, and so to do 1000kJ of work you burn more or less 1000kCal. 
Well if this is the case, I completely disagree with the display. On the screen, W, h:m:s and km are real and unquestionable (…more or less) then it should also display actual KJ not fancy wild ass guessed Kcal.
OTOH the idea of the pizza slices are ok because it is not on the same level as the other numbers, nor is it a scientific measure, but it is a rough translation of what the KJ burnt by the device would mean for our body. So I would understand the display of nnnKJ ~ nnn Pizza slices
Point taken, but to characterise it as a wild-ass guess is a bit of a reach. It’s a reasonable estimate, and any other software will likely use the exact same rule-of-thumb conversion. It should get you within 5% or so.
Here’s a pretty simplified article explaining it…it’s not just a guess.
I understand your point, but I believe it would be more accurate and indisputable to display the precise amount of kilojoules (KJ) and, alongside that, provide a translation into pizza slices or the equivalent in kilocalories (Kcal) burned for the benefit of the cyclists. I acknowledge that this may not be a matter of great significance, but rather a matter of utilizing the appropriate units.