The Apple Watch is already crushing the competition, according to new study

The Apple Watch officially went on sale less than six months ago, and it's already the second most popular wearable device on the market.

A new survey from the International Data Corporation (IDC) estimates that Apple shipped 3.6 million Apple Watches in the second quarter of 2015, putting it right behind Fitbit, which is estimated to have sold 4.4 million total units and has been selling wrist-worn fitness trackers since 2013.

The IDC's findings also suggests Apple shipped more units of its smartwatch than Xiaomi, Garmin, Samsung, and other gadget makers had of their respective wearables in the second quarter of 2015.

This is particularly significant because Apple hasn't spoken publicly about how many Apple Watch units it has sold since launch.

When asked about how many Apple Watches the company has sold, Apple's Jeff Williams told Re/code's Walt Mossberg the following in June: "A lot, but not enough. The only number I'll give you is that demand divided by supply is greater than one, and so that's all I've got for you, Walt. It's a lot."

The IDC also notes that two out of every three "smart" wearables shipped in the second quarter of 2015 was an Apple Watch. A "smart" wearable is a smartwatch or fitness tracker that's capable of running third-party applications, like the Pebble Time, Samsung Gear S, and Apple Watch.

That doesn't necessarily mean Fitbit isn't doing well. The fitness startup crushed expectations for sales and profit when it reported its second quarter earnings earlier this month, and it's still the market leader when it comes to wearables. Unlike the Apple Watch, which only works with the iPhone and starts at $350, Fitbit's wristbands come as cheap as $100 if you opt for an older model and they work with both Android phones and the iPhone.

They're more limited than the Apple Watch though, since they're primarily meant for tracking fitness rather than running apps.

Although we don't know exactly how many Apple Watches have been sold, most estimates and data from third parties seems to be positive. The one seemingly negative report came from Slice Intelligence in July, which said that interest in the watch had plunged since its launch.

The IDC's report also comes after Best Buy said earlier this week that demand for the Apple Watch has been "so high" that it's going to start selling the watch in all of its stores by the end of September. Apple has also said in the past that the Apple Watch sold better in its first nine weeks on the market than both the original iPhone and iPad did.