Need to charge a mobile device, or connect a peripheral to a PC or Mac? You’ll probably need to use some flavor of USB port, or a Thunderbolt port.

In their newest iterations, however, choosing between the two (or even just telling them apart!) can be confusing if you have a late-model PC or Mac. That's because of the emergence of the USB Type-C ("USB-C," for short) and Thunderbolt 3 interfaces in the last few years. These latest versions of Thunderbolt and USB share identically shaped connectors, and cables that are physically compatible with one another. But on laptops, desktops, and other devices, manufacturers don’t always offer labels that help you easily tell which is which. Sometimes, you're left to guess.

So, let's walk through the differences between these two interfaces, and explain which one you should use depending on which device you need to connect. 

What Is USB-C?

USB is an industry-standard connector for transmitting both data and power on a single cable. The USB-C connector looks similar to a micro-USB connector at first glance, though it's closer to oval in shape and slightly thicker to accommodate its best feature: flippability.

Like Apple's Lightning ports, the USB-C connector has no up or down orientation. Line up the connector properly, and you never have to flip it over to plug it in; the "right way" is always up. The standard cables also have the same connector on both ends, so you don't have to figure out which end goes where.

The USB-C connector was developed by the USB Implementers Forum (USB-IF), the group of companies that has developed, certified, and shepherded the USB standard over the years. The USB-IF counts more than 700 companies in its membership, among them Apple, Dell, HP, Intel, Microsoft, and Samsung. As a result, many new devices in a huge variety of tech categories come with USB-C ports. Hard drives, smartphones, and smart home devices all use USB-C for charging batteries, transferring data, or both.

Thanks both to wide adoption and an impressive range of capabilities, USB-C is quickly becoming a single port to rule them all. The oval-shaped port and associated connectors can transmit data at speeds up to 20Gbps (the exact speed ceiling depends on the specific USB SuperSpeed rating of the port) and deliver close to 100 watts of power to charge a device’s battery. In some cases, it can also transmit DisplayPort audio and video signals, letting you connect your device to an external monitor or TV. (The specific USB-C port in question needs to support DisplayPort over USB.)

Not every device with a USB-C port can do all of these things, of course. A USB hard drive can’t output a video signal. It simply uses USB-C for a bit of power and sending or receiving data, while an Apple iPad uses USB-C to charge its battery, sync with your PC or Mac, and output video. One port, lots of implementations and uses.

What Is Thunderbolt 3? 

Thunderbolt 3 ports look exactly the same as USB-C ports, and indeed, the connector is physically the same from a plug-in perspective. In many cases, they can do everything that a USB-C port can, except much faster. Indeed, Thunderbolt 3 is a superset of USB-C; you can plug a USB-C-only device into a Thunderbolt 3 port on a computer, and it'll work just fine.

Thunderbolt 3 lets you transfer data at up to 40Gbps. That's twice as fast as the 20Gbps maximum throughput speed of the fastest USB-C ports, and four times as fast as the original Thunderbolt interface. 

Not only can a Thunderbolt 3 port help you transfer data to and from a compliant external hard drive more quickly than a plain USB-C port, but it can also unlock additional capabilities for connecting external monitors and expansion docks. A USB-C port with support for Thunderbolt 3 means that a single cable is all you need to push power and transfer a large amount of information (such as video data for two or more 60Hz 4K external monitors) to and from a computer. 

Some companies have been quick to take advantage of these capabilities. Apple was among the earliest adopters of Thunderbolt 3 for computers, and now these ports are available on all late-model Mac desktops and laptops. Video-output capabilities depend on the system, but some iMacs can now support dual 6K Apple Pro Display XDR external monitors connected via Thunderbolt 3 cables.

More and more Windows PCs and peripherals are now coming with Thunderbolt 3 support, as well. You’ll find Thunderbolt 3 ports on many late-model premium ultraportable laptops, as well as a growing selection of external hard drives and expansion docks.

As noted above, Thunderbolt 3 ports on PCs are backward-compatible with USB-C devices. So, if you’ve got some peripherals that support Thunderbolt 3 and some that support only USB-C, they should both be able to work just fine on a Thunderbolt 3 port, albeit (in the case of the USB-C peripherals) limited by the slower speeds and capabilities of the USB-only device. 

How Can I Tell the Difference Between Thunderbolt 3 and USB-C Ports?

While a USB-C port that supports Thunderbolt 3 is clearly more capable than one without that support, it’s not always easy to tell the difference between the two.

The Apple MacBook Pro, depending on the model, has as many as four Thunderbolt 3 ports, but none of them bears labels or identifying markings of any kind—you’re just supposed to know that they’re all Thunderbolt 3 ports. The same is true of USB-C on some other devices, such as Microsoft’s Surface Laptop 3, whose USB-C ports don’t support Thunderbolt 3 but also go unmarked.

In such cases, the only way to tell what port you’re looking at is to read the product description on the website or packaging, or check the documentation. The same is true of cables. Some Thunderbolt 3 cables have bolts of thunder emblazoned on their oval-shaped plugs, while some don’t. Since you’ll need a Thunderbolt 3 cable to unlock all the capabilities of a Thunderbolt 3 port, a close read of the packaging materials is again in order. 

Many other Thunderbolt 3-equipped devices, especially laptops, have a mix of USB-C ports with and without Thunderbolt 3 capabilities. In those situations, there are usually clearly identifiable depictions of a bolt of thunder located next to the relevant ports.

Meanwhile, the USB-C ports that lack Thunderbolt 3 capabilities may be labeled with a USB SuperSpeed (SS) logo, along with a number indicating the peak speed of the port. Type-C ports that support charging over the port ("USB-PD," or USB Power Delivery) may appear with the SS logo in a battery icon. This breakout below from USB-IF shows how they look; reference the last two columns...

(Credit: USB-IF)

That said, USB-C/Thunderbolt 3 port labeling is inconsistent at best on modern PCs, especially laptops. In some cases, as mentioned, the port will just be unmarked, and the documentation for the device will be your best guide.

Which Port Should I Use: Thunderbolt 3, or USB-C?

While it might seem obvious that you should use the more advanced Thunderbolt 3 port over a regular USB-C one whenever you can, the decision isn’t always that simple. In many cases, you don’t even need to choose between the two at all. To see why, take the most basic capability of either port: charging a battery. On laptops that support charging their internal battery over USB-C, and that have a mix of USB-C-style connectors, some of which support Thunderbolt 3 and some that don’t, there’s often no difference between the ability of each port to charge the laptop's battery (though there are some exceptions).

Another situation in which Thunderbolt 3 and USB-C are interchangeable is when you’re connecting a client computer that supports Thunderbolt 3 (like a laptop) to a device that doesn’t (like a phone or external hard drive with a USB-C cable). In these cases, it will work, but the Thunderbolt 3 port on the laptop won’t make data transfers with the phone or drive any faster. 

But there are a few cases in which you should opt for Thunderbolt 3 where possible, even if that means opting for a more expensive device. This is mostly true for media professionals who frequently copy lots of images and video footage to and from external drives. For creative pros working on a late-model Mac, all of which support Thunderbolt 3, it’s a no-brainer to buy a Thunderbolt 3 external drive to reduce the time spent waiting for data transfers to complete. 

As a result, neither Thunderbolt 3 or USB-C is a clear winner. They’re just different, and each one excels in different use cases. Ultimately, if the history of interface evolution is any indication, they’ll both be replaced by a new standard in a few years—perhaps the fledgling USB4—and there will be a whole new set of differences to learn, and subtleties to unravel.