The Apple Watch Series 11 is the most accurate smartwatch heart rate monitor you can buy right now. In controlled testing against a Polar H10 chest strap, it stayed within 1% of the chest strap’s readings during runs, beating every other major smartwatch by a significant margin. The Garmin Venu 4 came in second at 3.89% error, followed by the Google Pixel Watch and Samsung Galaxy Watch at 5.6% and 6.6% respectively.
How the Top Smartwatches Compare
CNET Labs tested five major smartwatches over 30 miles of running, using a Polar H10 chest strap as the benchmark. That chest strap correlates above 0.93 with medical-grade ECG readings during exercise, making it the closest thing to a clinical reference outside a hospital. Here’s how the field stacked up:
- Apple Watch Series 11: Within 1% of the chest strap. Consistently strong across every workout category.
- Garmin Venu 4: 3.89% error rate (about 5.5 bpm off). Records heart rate every second, matching the chest strap’s sampling frequency.
- Google Pixel Watch: 5.6% error rate. Tended to catch up to the chest strap’s readings over time, meaning longer runs produced better results.
- Samsung Galaxy Watch: 6.6% error rate. Similar catch-up pattern to the Pixel Watch on longer efforts.
All four watches stayed within 8% of the chest strap, which is respectable. But the gap between Apple’s 1% and Samsung’s 6.6% is meaningful if you’re using heart rate zones to guide training intensity or tracking cardiovascular fitness trends over time. At a heart rate of 160 bpm, a 1% error means you’re off by less than 2 beats. A 6.6% error puts you off by more than 10.
Why Sampling Rate Matters
The Garmin Venu 4 records your heart rate every single second. The Apple Watch samples every five seconds. On paper, Garmin’s approach sounds better, and for activities with rapid heart rate changes (like interval training or circuit work), more frequent sampling can capture spikes and drops that a five-second interval might miss. But in practice, the Apple Watch’s algorithm compensates well enough to still produce the lowest overall error rate.
This distinction matters most during high-intensity interval training. Garmin’s latest sensor generation (Elevate Gen 5, found in the Fenix 7 Pro, Venu 3, and Forerunner 965 as well) tracks within 1 to 3 bpm during steady efforts and 3 to 6 bpm during sprints and intervals, with only a 1 to 2 second response lag. If your workouts involve lots of rapid pace changes, Garmin’s faster sampling gives you a more responsive real-time display even if the Apple Watch edges it out on cumulative accuracy.
What Makes One Sensor More Accurate Than Another
Every smartwatch uses the same basic technology: LEDs shine light into your skin, and photodiodes measure how much light bounces back. Your blood absorbs light differently depending on how much is flowing through your vessels with each heartbeat. The watch’s algorithm interprets those fluctuations to calculate your pulse.
The differences come down to hardware and software working together. More LEDs at multiple wavelengths (green, red, infrared) give the sensor more data to work with. Better algorithms filter out noise from wrist movement, arm swing, and vibration. Garmin’s Gen 5 sensor uses multi-band LEDs and has evolved through five hardware generations to reach its current accuracy. Google’s Pixel Watch 3 improved its readings not by changing its sensor hardware but by updating its algorithm to account for arm swing and ground contact during running. In testing, the Pixel Watch 3 initially deviated by 3 to 4 bpm at the start of a run but settled to within 1 bpm for most of the session.
Apple hasn’t published detailed specs on its sensor, but the third-generation optical heart rate sensor (used in the Series 10 and Ultra 2) delivers about 87% of exercise readings within 5 bpm and 95% within 10 bpm. The Series 11 appears to have improved on this further based on the CNET testing data.
Skin Tone Can Affect Readings
Optical heart rate sensors are less accurate on darker skin tones. Melanin in the skin’s outer layers absorbs more light, reducing the signal that reaches deeper blood vessels where the actual pulse measurement happens. This is a known limitation across all brands, not specific to any one watch.
Researchers are working on solutions. One promising approach uses polarized light to distinguish between signals from superficial skin layers (where melanin interferes) and deeper blood vessels. In early testing across light, medium, and brown skin tones, this polarization technique consistently produced stronger pulse signals, with the biggest improvement at darker skin tones. This technology hasn’t reached consumer products yet, but it signals that future watches will likely narrow this accuracy gap.
If you have a darker skin tone and want the best readings possible right now, wearing the watch snugly (but not tight) about a finger’s width above your wrist bone helps. A chest strap remains the most reliable option when accuracy really matters, regardless of skin tone.
Resting vs. Exercise Accuracy
Smartwatches are generally more accurate at rest than during movement. When you’re sitting still, there’s no arm swing, no vibration, and no bouncing to confuse the sensor. Most modern smartwatches from Apple, Samsung, Garmin, and Google perform well for resting heart rate and sleep tracking. The real differences emerge during exercise, especially high-intensity or interval-based workouts where your heart rate changes quickly.
The catch-up pattern seen in the Pixel Watch and Galaxy Watch during CNET’s testing illustrates this well. Both watches struggled more in the early minutes and during pace changes but gradually aligned with the chest strap during steady-state running. If you primarily use heart rate data for resting trends, sleep quality, or recovery tracking, the differences between watches matter less than they do for serious athletic training.
ECG Features Are a Separate Category
Heart rate monitoring and ECG are different things. Continuous heart rate tracking uses optical sensors and runs passively throughout the day. ECG requires you to touch a specific point on the watch to complete an electrical circuit, producing a single-lead electrocardiogram. The FDA has cleared several smartwatches to detect atrial fibrillation using ECG: the Apple Watch (Series 4 and later), Samsung Galaxy Watch 4 and later, Fitbit Sense, and Withings ScanWatch.
These ECG features are designed to flag irregular heart rhythms, not to provide more accurate heart rate numbers during a workout. If your concern is detecting an arrhythmia, any of these FDA-cleared watches can serve that purpose. If your priority is accurate heart rate tracking during exercise, the optical sensor performance matters more, and the Apple Watch Series 11 leads that category.
Which Watch to Buy for Your Needs
For pure heart rate accuracy during workouts, the Apple Watch Series 11 at $400 is the clear winner. It posted the lowest error rate across all exercise categories in head-to-head testing.
If you want the fastest real-time response and already use Garmin’s training ecosystem, the Venu 4 or any Garmin watch with the Elevate Gen 5 sensor (Fenix 7 Pro, Forerunner 965, Venu 3) gives you second-by-second tracking with excellent accuracy. The 3.89% error rate is still very good, and the one-second sampling is a real advantage for interval training.
If you’re a casual exerciser who mostly cares about daily trends, sleep data, and step counts, any current-generation watch from Apple, Google, or Samsung will give you reliable enough heart rate data. The accuracy gaps between these watches shrink considerably at rest and during steady, moderate exercise. Where you’ll notice the difference is during intense, variable workouts where every beat per minute counts for training decisions.