Thunderbolt vs. USB-C: What’s the Difference?

Note: WSD asks for a mention of 2019's still-not-available USB4, which is supposed to merge the interfaces, somewhere and link to a USB4 article

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 just telling them apart—can be confusing. That's because of the emergence of USB Type-C (usually called USB-C), Thunderbolt 3, and Thunderbolt 4 interfaces in recent years. These three specifications share identically shaped connectors and cables that are physically compatible with one another. But laptop, desktop, and device manufacturers don't always provide labels that help you easily tell which is which.

Instead of leaving you to guess, let's walk through the differences between Thunderbolt and USB-C, and explain which one you should use depending on which device you need to connect. 

What Is USB-C?

The Universal Serial Bus is an industry-standard connector for transmitting both data and power on a single cable. The USB-C connector looks similar to the older micro-USB connector at first glance, though it's more oval in shape and slightly thicker to accommodate its best feature: flippability. Unlike the rectangular USB Type-A, a USB-C connector has no right side up or upside down; you just line it up and plug it in. The standard cables also have the same connector on each end so you needn't wonder which end goes where.

A Thunderbolt 4/USB-C port on an Apple iPad Pro
(Credit: Molly Flores)

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. There are more than 700 USB-IF member companies, including Apple, Dell, HP, Intel, Microsoft, and Samsung. As a result, many new devices in a variety of tech categories now sport USB-C ports. External hard drives, smartphones, and smart home devices all use USB-C for charging, transferring data, or both.

Thanks to its wide adoption and impressive range of capabilities, USB-C has quickly become one port to rule them all. The oval-shaped connector can transmit data at speeds up to 20Gbps (the exact ceiling depends on the port's specific USB SuperSpeed rating) and deliver nearly 100 watts of power to charge a phone's, tablet's, or laptop's battery. In some cases, USB-C can also transmit DisplayPort audio and video signals for connecting your device to an external monitor or TV. (The port in question needs to support a standard called DisplayPort over USB(Opens in a new window).)

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 power and data transfer. An Apple iPad uses USB-C to recharge, sync with your Mac or PC, and drive an attached monitor. One port, lots of implementations and uses.

What Is Thunderbolt? 

Thunderbolt 3 and Thunderbolt 4 ports look exactly the same as USB-C ports, and indeed their connectors are physically identical. For the most part, they can do everything a USB-C port can, except faster. Indeed, Thunderbolt is a superset of USB-C; you can plug a USB-C device into a Thunderbolt 3 or 4 port on a PC and it'll work just fine.

Today's Thunderbolt 4 devices let you transfer data at up to 40Gbps—twice as fast as the 20Gbps maximum throughput of today's fastest USB-C ports, and four times as fast as the original Thunderbolt interface. Besides sending and receiving data to and from an external hard drive, Thunderbolt can unlock additional capabilities for connecting displays and expansion docks. A Thunderbolt port 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 resolution external monitors) to and from a computer. 

An external hard drive with a USB-C port
(Credit: Zlata Ivleva)

Companies have been quick to take advantage of these capabilities. Apple was among the earliest adopters of Thunderbolt 3, and Thunderbolt 4 is available on all late-model Macs as well as the iPad Pro. Video output capabilities depend on the system, but some iMacs support dual 6K Apple Pro Display XDR monitors connected via Thunderbolt cables. You'll also find Thunderbolt 4 ports on many—though not the cheapest, and primarily on Intel- rather than AMD-powered—Windows laptops and a few desktops, as well as a growing selection of external hard drives and expansion docks. 

Thunderbolt 4 isn't radically different from Thunderbolt 3; both use identical USB-C connectors and share the same 40GBps top speed. The newer spec supports sending video signals to two 4K displays or one 8K display, where Thunderbolt 3 permitted only a single 4K monitor, and doubles the supported PCI Express data rate to 32Gbps.

As noted, Thunderbolt ports are backward-compatible with USB-C devices. So if you've got some peripherals that support Thunderbolt and some that support only USB-C, both should be able to work just fine with a Thunderbolt port, though the USB-C peripherals will be limited to USB-C speeds and capabilities.

How Can I Tell the Difference Between the Ports?

While a USB-C port that supports Thunderbolt is more capable than one that doesn't, it's not always easy to tell the difference between the two. Apple's MacBook Pro and MacBook Air laptops have as many as four Thunderbolt ports, but none of them bears a label or identifying markings of any kind—you're just supposed to know that they’re all Thunderbolt ports. The same is true of some other devices' USB-C ports.

The Microsoft Surface Laptop's USB-C port does not have a label.
(Credit: Zlata Ivleva)

In such cases, the only way to tell what you're looking at is to read the product specifications on the packaging or manufacturer's website or check its documentation. The same goes for cables. Some Thunderbolt ports and cables have little lightning bolts emblazoned on them, while others don't. Since you'll need a Thunderbolt rather than USB-C cable to unlock all the capabilities of a Thunderbolt port, a close read of the packaging is again in order. 

(Credit: Zlata Ivleva)

Many other devices, especially laptops, have both USB-C and Thunderbolt 4 ports, usually identified with USB and lightning-bolt symbols respectively. That said, USB-C and Thunderbolt labeling is inconsistent at best.

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

While it might seem obvious that you should use the faster, more capable Thunderbolt rather than USB-C, the decision isn't always that simple. In many cases, you don't 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 recharging over USB-C and have both USB-C and Thunderbolt connectors, there's usually no difference between the ability of a given port to charge the system (though there are some exceptions(Opens in a new window)).

Another situation in which Thunderbolt and USB-C are interchangeable is when you're connecting a client computer that supports Thunderbolt (say, a laptop) to a device that doesn't (say, a phone or external hard drive with a USB-C cable). In these cases, the device will work but the laptop's Thunderbolt port won't make data transfers any quicker. And many peripherals, such as printers, mice, and keyboards, don't need the full speed of USB, let alone Thunderbolt.

(Credit: Zlata Ivleva)

But there are cases in which you should opt for Thunderbolt 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 a creative pro with a Thunderbolt-equipped computer, it's a no-brainer to buy a Thunderbolt instead of USB-C external drive to reduce the time spent waiting for data transfers to complete. 

Overall, neither Thunderbolt or USB-C is a clear winner. They're just different, and each excels in different use cases. Ultimately, if the history of hardware interfaces is any guide, they'll both be replaced by a new standard in a few years—perhaps the fledgling USB4—and there'll be a whole new set of differences to learn and subtleties to unravel.