A new report from IDC estimates that Apple sold about 3.6 million Apple Watch units in the second quarter of 2015. This would put them behind Fitbit, the market leader, which shipped 4.4 million of its various bands in Q2. In shipping 3.6 million watches, Apple is estimated to have captured 19.9% of the wearable market. In total, wearable manufacturers are said to have shipped about 18.1 million units.
Apple also reportedly captured nearly two-thirds of the smart wearables category, with smart wearables defined as wearable devices running third-party apps. From StreetInsider:
"About two of every three smart wearables shipped this quarter was an Apple Watch," said Jitesh Ubrani, Senior Research Aanalyst for IDC Mobile Device Trackers. "Apple has clearly garnered an impressive lead in this space and its dominance is expected to continue. And, although Fitbit outshipped Apple, it's worth noting that Fitbit only sells basic wearables – a category that is expected to lose share over the next few years, leaving Apple poised to become the next market leader for all wearables."
Apple has not yet provided sales numbers for the Apple Watch, saying only that it was performing well. Estimates placed around the launch of the watch indicated that around 2.3 million watches had been pre-ordered initially.
In the beginning, the Apple Watch was only available online, then limited to Apple Stores for its retail launch. The watch only started showing up in mainstream third-party retailers in early August. With more customers now able to get their hands on the watch before they buy, it wouldn't be surprising to see Apple's numbers in the wearables market continue to grow.