Zwift calories - how accurate

Hi folks, newbie here, only been zwifting for 5 days on Tacx Flux 2. Was wondering how accurate the calories burned in zwift? I’ve been putting 20-40km or around 1-2.5 hours on saddle. In the real world, for 2 hours training I would’ve burned around 1200-1300 cal. Using Garmin Edge 520 plus, cadence + HRM strap. In zwift for 2.5 hours ride, I’ve only burned around 800kcal.

I havent compared it directly with the Garmin indoor since I cannot wear 2 HRM strap at the same time… At least I dont think its doable. However, I have compared it to my huawei watch. Both reports same average HR. BUt at the end of the ride, zwift shows I burned around 600ish kcal and the watch shown 800ish kcal with indoor cycle mode selected on the watch.

Just how accurate the calories burn numbers in zwift based on your experience? Which one I should use as benchmark for my diet? Thank you

Everything is an estimate, but if you’re using a power meter (which you are) then Zwift uses a conversion of equivalent energy burned to produce the actual watts you have put out during the ride. As such it’ll be far more accurate than anything estimated from your heart rate, or worse still based on just your height/weight/age.

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thanks. so you are saying that the calories burned is more accurate on the zwift vs my watch or my outdoor ride?

Much more accurate. That’s not to say it’s perfectly accurate because it’s still based on an estimate of your body’s efficiency in converting energy to watts, but it’s at least using an actual measurable output rather than just guessing. Your watch has no idea how much power you’ve been putting out. Zwift (via your power meter) does. If you bought a power meter for your outdoor rides, a crank or pedals for example - they’d also show a much more accurate number, for the exact same reason.

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damn, that would mean i would need to put out at least 30% more effort and/or time to burn 800 calories. it’s tough, but achievable. just need more time and practice.

and all along i’ve been “duped” by misleading numbers.

thanks for the explanation Dave. appreciate that

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As I recall, Zwift is certainly (and deliberately) at the lower end of the energy conversation estimate. But I would argue that’s the better way around anyway. Much better to outdo what you thought than be fooled by overestimated numbers.