Garmin Vs Zwift calories way off

Hi all,

Newcomer to zwift as I start to rebuild my confidence on the bike after an injury.

I have my bike rigged up to a Cycleops Fluid 2, and Garmin speed and cadence 2 sensors. My HR is transmitted from my Garmin Venu.

I just had a great ride doing the welcome Fondo workout. But my calorie measurements are way off. Garmin is 588 zwift 398. Which should I trust? And why might this happen?


Check your weight, height and gender on both. They both would use a different formula, it’s all guesstimation anyway.


^^ What Ben said - calories burned are just estimates on any app. IMO, it’s better to choose one app and stick with it to track your fitness goals long-term.

I know. Similar with me today. Using wahoo tickr With a Garmin computer which said nearly 1000 calories which I can believe and Zwift says less than 400! What is the point in asking you to connect a HRM if Zwift is going to ignore it essentially and give a completely baseless calculation based on power. I’ve hear responses that Zwift relies on power to calculate calories burned…well if the algorithm is meant to be so good why is it way off reality.

FYI, it doesn’t matter the algorithm, it’s a best guess on the amount of calories burnt.

Both Zwift and Garmin (and any other) is not correct. There is no reliable way to accurately measure calories burnt.

It will depend largely on what sensors you have paired and if they are all paired to both zwift and the garmin.

If either has a powermeter attached that’ll likely be nearer the actual amount but as others have said it is all a bit of a guesstimate.

If your goal is weightloss then best advice is to go with lower one if trying to balance diet and exercise.

I use a power meter. Looking at my most recent ride on Zwift, totalling 1:46 hours and about 40km my stats were…

Zwift calories = 668 (warm-up + main ride)
Garmin calories = 696

I won’t lose sleep over the difference.


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Well, there is actually if you are using a power meter… at least, you should be able to get within a few percent which is far better than most other exercises. Very briefly and oversimplified, just look at your power output in kJ … that’s essentially your calorie burn.

There are several articles online that discuss why this is and I won’t belabor it, but if your device says you burned 1000 calories and you only put out 500kj total for example, something is very wrong. With a 500kj output, the calorie range should be between 480-520, which is a pretty tight margin. On the lower side if in good shape, or higher side if not. Can there be exceptions? Sure…

Naturally this assumes you have an accurate power meter, which is often not the case. A HR meter can help hone this in. Live example: just did a ride where I output 875kj. I’m in pretty good cycling shape, so in looking at my calorie burn and HR data, zwift/Strava says 848 kcal. That checks out. About as close as you can get without true medical equipment.

I’m not a medical expert, but I’ve read a lot in my training to try get a better understanding. We are pretty fortunate in cycling to have some decent ways to reasonably gauge effort.

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Are you using a power meter? How many kJ did you burn total in the ride and over what time frame?

EDIT: being curious I looked up your profile. Looking at the ride from earlier today, which was just over an hour, you had an avg output of ~103w. That would mean you generated 384kJ over the ride. If you are using a power meter and it is accurate (big if!), I hate to say it but zwift is the accurate one here. There is no way you can burn close to 1000 calories.

So, the device that said you burned 1000 calories is either ignoring your power data, or something is really off on your power meter.

Don’t shoot the messenger, but power data (if the meter is accurate) is the best way to calculate burn.

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It’s still just a best guess.

Take calories burned with a grain of salt on any platform or device, but kilojoules/work done is a pretty useful metric.

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Of course. My GPS location is a best guess as to my true location but close enough to trust it.
While I’m giving my TED talk here, I’ll also say: given that calorie counts in the food we’re consuming can be off by 20% compared to what is on the label, and given most people rarely measure/weigh food, it’s not worth worrying over a few % accuracy on calorie burn.