Calories burned lower than kj output - possible?

I’m noticing for my outdoor rides on Strava that my calories burned around 200 to 300 less than total kj.

Is this possible? Indoors on TR for example my calories are calculated around 1:1 with kj as expected.

I’m uploading through Wahoo with a bolt. Any reason for this?

Are your outdoor rides with a power meter? If not it’s hard to trust the calorie values from Strava/Garmin/Wahoo.

I think Strava and TR calculate the Calories burned a little bit different.

To clarify the different units.
1 cal ≡ 4.18 J
But in a nutrition context, you use Calorie instead of kilocalrie (1000 cal).
So in a Nutrition context 1 Cal (normaly with a capital C) is equal to 4.18 kJ (4’180 J).

The physikel work your legs did during a ride is given you in kJ, but your body burns a lot more then just what you pushed in the pedals, ruffliy 4 times more. But this varies from person to person (in a range of 5 to 4).
This 4 times bigger value is then displayed as Calories, what is nearly a 1:1 ratio.
So TR may take 4 times the energy you produced and Strave only 3.9.

For a more detailed desciption you can read the TR article:

Are you using HR data? When I have a low hr average, calories from garmin etc… are super low.

Thanks guys, had no internet for a bit there. Yes I’m using HR monitor. I did a ride outdoors yesterday without it and the calories calculated were now a few hundred higher than the kJ output. So guess it’s Hr and or strava algorithms that are causing this. I’ll jiust ignore and keep my eye on the KJ for calorie counting…

Based on my experience with always using a hr monitor on the bike the calories are based on the hr which depending on where it is your output will be off.