IDC estimates Apple shipped around 3.9 million Apple Watches in the September quarter. The research firm released that number as part of its estimates for the wearables market, which it published on Thursday.

IDC: Apple Shipped 3.9 Million Apple Watch Units in September Quarter

The figure is up 300,000 units from IDC’s estimates for the June quarter, giving it a slight increase from quarter to quarter. The figure gives Apple an estimated 18.6% share of the wearables market. Most of the growth can be credited to Apple’s international expansion for sales of the device, along with it finally making the product available via third-party retailers.

IDC says the public has shown the greatest interest in the Sports model of the Watch, which can be expected, as it is the most reasonably priced of all of the Apple Watch models. IDC says that explains Apple’s decision in September to begin offering gold and rose gold color options for the Sport model.

Apple’s 3.9 million shipped was good for only second place in the wearables market, as FitBit shipped 4.7 million units of its popular fitness trackers to take first. Xiaomi showed up in third, with 3.7 million units, while Garmin (900,000 units), and XTC (700,000 units) filled out the top five. Garmin focuses its product on serious fitness enthusiasts, while XTC sells only in China.

It should be noted that Apple does not announce official sales numbers for the Apple Watch, so all of IDC’s numbers are just estimates. In the past, estimates from various sources have conflicted greatly, so IDC’s numbers should be considered in that light.