Garmin calories worst among four brands, science shows

Garmin calories worst among four brands, FIU science shows

A study in PLOS One found that Garmin’s calorie counts were the least accurate of four major smartwatch brands with a 77.6% error. Researchers at Florida International University tested the Apple Watch Series 8, Fitbit Sense 2, Samsung Galaxy Watch 5, and Garmin Forerunner 955 against a COSMED K5, a lab machine that measures real calorie burn from a person’s breathing.

Fifty-eight adults completed a ten-minute interval session on a recumbent exercise bike, alternating two-minute blocks between 64 to 76 percent and 77 to 95 percent of their estimated maximum heart rate. Each wore all four watches at once, with wrist positions rotated to cancel out any placement bias.

Here’s how the four watches compared, worst to best, as a share of the real calorie count:

Garmin’s 68.61 kcal average miss most likely falls somewhere between 53 and 84 kcal, a wider range than any other brand tested.

Fitbit’s average miss of just 3.14 kcal looks clean, but only because researchers threw out seven readings that were wildly wrong, some more than four times the real value, about one in eight of its results. Put those back in, and Fitbit’s average miss jumps to 128.6 kcal, worse than Garmin’s 68.61 kcal. Fitbit also failed to record a calorie count at all in one session.

The error grew alongside body fat for every device, but it grew faster for Garmin and Fitbit than for Apple. Skin tone, tested across three shades common among Hispanic adults, made no measurable difference to accuracy.

Garmin’s watch failed to produce a reading once, Samsung’s twice, Apple’s never. After removing unusable results, 51 of the original 58 Garmin readings remained, against 52 for Apple, 50 for Samsung, and 44 for Fitbit.

the5krunner’s own testing found a similar pattern in a different Garmin product: in a CIRQA (2026) band review, its calorie count swung from second-lowest of four wearables on one day to highest on another, the least consistent of the group, though that test had no lab reference to measure against.

The full dataset sits on the study’s OSF page. Its authors say none of today’s consumer watches measure calories reliably enough for weight management or research, though they note the numbers may still help track how one person’s own readings shift over time.

Potential Flaw

As @DanielH points out, virtually none of these studies insist on getting a correct HRmax and VO2max into the watch’s ecosystem. Sure, the actual calories measured by the COSMED K5 are probably right, but Garmin’s algorithms use HRmax and VO2max. That said, the subjects are likely not athletes, and population estimates applied to their VO2max and HRmax might be reasonable.

Take Out

This research probably showed that Garmin had the worst calorie estimate of the brands tested. Worse still, that poor estimate became poorer the higher the subject’s body mass index. i.e. it’s even worse for the people most likely to be relying on their smartwatch’s calorie counting.

For once, the scientists here seem to be using a sensible array of test devices. Garmin Forerunner 955 (2022) is a representative one of the brand, albeit using the Elevate Gen 4 sensor (which I show as reasonably accurate in my recent Forerunner 170 review)

Quick answers

Which smartwatch was worst at counting calories in the study?
Garmin’s Forerunner 955 had the largest error of the four watches tested, both in raw kcal (a 68.61 kcal average miss) and as a share of true calories burned (77.6 percent), ahead of Samsung, Apple, and Fitbit.

Is Fitbit better than Garmin at counting calories?
Only if you ignore Fitbit’s worst readings. Put them back in, and Fitbit’s average miss jumps to 128.6 kcal, worse than Garmin’s 68.61 kcal.

Does body fat affect how accurate a smartwatch's calorie count is?
Yes. Every watch got less accurate as body fat rose, and Garmin and Fitbit got worse faster than Apple did.

Last Updated on 3 October 2026 by tfk the5krunner

tfk the5krunner

tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID