I raced a half marathon with the Apple Watch Ultra 4 vs Apple Watch Series 12 to test accuracy — here’s what happened

The Apple Watch Ultra 4 and Apple Watch Series 12 underwent a real-world test during the Shoreditch Half Marathon, a race renowned for its tight turns and twists. The race route, slightly exceeding the official 13.1-mile distance, provided an ideal setting to assess GPS accuracy. Both watches were paired with a Garmin HRM-600 chest strap heart rate monitor and a Coros Pace 4 Pro sports watch for comparative purposes.

When it came to GPS accuracy, the Ultra 4 took the lead, closely mirroring the Coros Pace 4 Pro's track, thanks to its multi-band GPS system. The Series 12, while still reliable, showed more minor errors, such as veering off roads due to its smaller GPS system. Despite the potential for a longer distance due to the race route, the Ultra 4 and Coros Pace 4 Pro both logged 13.31 miles and 13.22 miles respectively.

Heart rate accuracy was another factor in the comparison. The Series 12 consistently provided accurate heart rate readings, even in the early stages of the race, while the Ultra 4 required a few minutes to establish a reliable reading. This difference could be attributed to the watches' design and fit, with the Series 12 offering a snugger fit on thinner wrists, ensuring consistent heart rate tracking.