The Garmin Fenix 9 Pro and Apple Watch Ultra 4 are two of the best (and most expensive) smartwatches to come out this year. But just how accurate are they?
Much has been made of Apple's redesigned Health Sensing System, supposedly the most accurate ever on a wearable. It certainly measured my sleep well enough, and Apple says it tested its accuracy by pitting it against an electrical heart rate monitor — which, funnily enough, is my process for reviewing smartwatches too.
I set out to find out how accurate Apple and Garmin's best smartwatches were by putting them against each other in a head-to-head battle, wearing them both during a 30-minute run, one on each wrist. To create a benchmark, I wore an ECG-capable electrical heart rate monitor on my chest, just like Apple's own tests; I used the Frontier X2.
The 30-minute run was more challenging than usual, because it was a very hilly route with a long incline as the midpoint — it certainly made my heart rate spike.
The figure I'm most interested in during these tests is average heart rate. I recognize that different companies use different processing algorithms, so you'll never get a 1-1 match on all heart rate data points: all you can look for is consistency in your wearable of choice, and to make sure it's generally telling the same story as a benchmark-level tool such as a chest-mounted electrical HRM, which are generally more reliable than LED-based sensors.
The closer the average heart rate, calculated by the wrist-based LED-using wearables, can get to the average heart rate calculated by the electrical HRM, the better.
Generally, I classify under 5 bpm of difference as an insignificant margin of error, meaning that's a device I'd happily keep using and recommending to others. Under 10 bpm is generally fine for light or occasional exercisers for general trends, but not one I'd recommend to fitness buffs who care about things like heart rate zones.
Anyway, on to the results — how did the Apple Watch Ultra 4 and Garmin Fenix 9 Pro stack up?
The results
The results were excellent. It’s really cool to see the Frontier X2 heart rate monitor, Garmin Fenix 9 Pro and the Apple Watch Ultra 4 all within two beats per minute of each other on average.
From left to right in the screenshots above, the Garmin Fenix 9 Pro measured 159 bpm, while the Apple Watch Ultra 4 measured 160 bpm. The Frontier X2 measured 158 bpm.
Wearable |
Average heart rate (bpm) |
Frontier X2 HRM |
158 |
Garmin Fenix 9 Pro |
159 |
Apple Watch Ultra 4 |
160 |
All the devices being within 2 bpm of each other is a wonderful indication of accuracy across the board. Algorithmic processing differences aside, all three devices are telling the same story about my body during that 30-minute session of exercise.
Other metrics between the two watches are similar, too. Calorie counts for example, which can vary wildly between devices, look similar as both devices estimate a burn in the high 300s — 388 vs 375.
The Frontier X2 also estimates a calorie count that's very different than the watches, but I'm discounting that as the watches collect far more information to draw from. I'm only trusting its heart rate numbers.
So, I'm more than happy with the ratings I got from these watches, and can continue to recommend them as extremely accurate health and fitness tracking tools.
So, which do I prefer? Even though both watches are very accurate, they're tailor-made for serious sports and endurance, and they're both packing dive modes and satellite communication features, they're not quite made equally.
The Apple Watch's software, third-party apps and smartwatch functionalities far outshine the Garmin Fenix 9 Pro, while the Garmin watch is built with a longer-lasting battery (10 days vs Apple's 48 hours) and features more survival tools, such as the LED flashlight.
If you're a multi-day adventurer type, I'd opt for the Garmin every time, but for day-to-day wear and shorter excursions, the Apple Watch is nicer to use — even if, unfortunately it'll need a charge every other day.
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