Calories Burned in an Indoor Cycling Class

8.5 METs. That’s the value exercise science assigns to a spin-style indoor cycling class, according to the Compendium of Physical Activities. With that number, you can calculate what you actually burned — more accurately than any bike screen.

Because the screen, at the end of class, almost always says something else: 600-something kcal. It looks like a receipt, a precise figure. It’s a generous estimate: a generic formula that doesn’t know your body composition, your pedaling efficiency, or how much real effort you put into the pedal.

Here’s where each number comes from, and which one you should actually believe.

Where the number on the screen comes from

Measuring real energy expenditure requires analyzing the oxygen you consume and the carbon dioxide you exhale, something done in a lab with specialized equipment, not on a studio bike. What the screen does is estimate, using generic formulas based on speed, resistance, and sometimes a body weight you entered yourself at the start of class (if you entered it correctly).

The result is a number that tends to run high. There’s no bad intent here: it’s a technical limitation of any estimate that doesn’t directly measure your body.

A more realistic calculation, with simple math

That 8.5 comes from METs (metabolic equivalents), the standardized way exercise science estimates the energy cost of an activity. The most widely used version is the Compendium of Physical Activities (Ainsworth and colleagues, 2011, Medicine & Science in Sports & Exercise), the reference table that assigns that 8.5 MET value to a spin-style indoor cycling class.

Using the standard formula for estimating energy expenditure (METs × 3.5 × weight in kg ÷ 200 = kcal per minute), a person weighing about 65 kg who takes an intense 45-minute class burns approximately 360 to 435 kcal, depending on how consistently they held the intensity. Not 600. Not 700. And if you weigh more or less, or if your real effort was moderate instead of intense, the number moves in both directions.

This isn’t meant to make the class feel like it’s “worth less.” It’s the number you can actually defend if someone asks, instead of the one the screen inflates.

For context: 8.5 METs is an intensity similar to running at a steady pace, well above walking. It makes sense that a well-run cycling class, with real resistance climbs, feels demanding. The MET number isn’t low. What’s inflated isn’t the effort — it’s the translation of that effort into an exact calorie figure.

Source: 2011 Compendium of Physical Activities: A Second Update of Codes and MET Values — Ainsworth and colleagues, 2011

Why your watch or fitness tracker doesn’t get it right either

If you trust your smartwatch instead of the bike, the news isn’t any better. A Stanford study (Shcherbina and colleagues, 2017, Journal of Personalized Medicine) tested seven commercially available wrist devices (including Apple Watch and Fitbit, among others), comparing their estimates against lab measurements. The watches measured heart rate reasonably reliably. Energy expenditure was a different story: the most accurate device was off by an average of 27%; the least accurate, by 93%.

Even the best watch in that study blew past the margin of error anyone would consider acceptable. If your tracker says 400 and your bike says 600, neither one is the absolute truth: both are estimates, just with different degrees of error.

Source: Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort — Shcherbina and colleagues, 2017, Journal of Personalized Medicine

Why your heart rate doesn’t tell you how many calories you burned either

It’s easy to assume that if your heart rate stayed high the whole class, you burned a lot of calories. It’s not that direct. Heart rate is an indicator of how hard your heart is working, not a direct measurement of energy spent: two people with the same heart rate can be burning different amounts of energy, depending on fitness level, age, body composition, and even the room temperature.

In fact, the same Stanford study cited above found something telling: wrist devices measure heart rate with far more precision than they manage when translating that heart rate into a calorie number. The problem isn’t measuring pulse (that’s already done reasonably well); it’s translating that pulse into energy expenditure, a step that depends on variables a wrist sensor can’t see.

So if your class felt intense and your heart rate was high, that tells you that you worked hard, which is, in the end, what matters most for the health benefits. Don’t use that same figure to precisely calculate how many calories you burned: they’re two different questions, even though the device shows them together on the same screen.

The real benefit shows up with consistency, not in a single class

Chasing the number from one random class is the wrong question. The evidence shows that the benefit of indoor cycling shows up with regular practice, not with a single isolated session.

A systematic review (Chavarrias, Carlos-Vivas, Collado-Mateo, and Pérez-Gómez, 2019, Medicina, Kaunas) analyzed 13 studies with 372 participants and found improvements associated with consistent indoor cycling practice in aerobic capacity, blood pressure, lipid profile, and body composition. None of those changes show up in a single class; they build up over weeks of regular attendance.

Source: Health Benefits of Indoor Cycling: A Systematic Review — Medicina (Kaunas)

So what’s the point of looking at the number on the screen?

As a quick reference, not mathematical truth. If it helps you compare one of your own classes against another of your own, not against someone else’s or against what an ad promises, use it that way: as a trend, not an exact figure.

What actually moves the needle is showing up regularly, keeping genuine effort during class (not just pedaling easy while watching the number climb), and letting the adaptations happen over weeks, not in one session.

FAQ

Why does the class bike show more calories than what I calculate myself?

Because it estimates with generic formulas, not a real measurement of your body. It tends to run high. The MET-based calculation from the Compendium gives a more conservative, more defensible number.

Is my smartwatch more reliable than the bike?

Not necessarily. Studies that have compared wrist watches against lab measurements find large errors in energy expenditure, even though heart rate itself is usually measured with more precision.

How many calories do I burn in a Naü Cycle class?

It depends on your weight and your real intensity. Naü Cycle runs 45 minutes: someone weighing about 65 kg in an intense class is in the range of 360 to 435 kcal, not 600.

Our recommendation: next time you finish a Naü Cycle class, ignore the number on the screen and go by your perceived effort, measured against your own past performance. If it’s your first time on a studio bike, here’s what to expect so you don’t walk in blind — our coaches also cue in English, which makes that first ride easier if Spanish isn’t your first language.