“USB” or Universal Serial Bus is a standard that was created as a means to make connectors more universal and transparent. USB C is a specific shape of USB connector and was designed to take that universality a step further by being the one connector for almost anything including data, power/charging, video and audio. The connector is also reversible, it has no up or down orientation!

While USB C does make some things a lot easier, there is also lots of confusion and uncertainty surrounding it. Are all USB C cables the same? (No). What can USB C do that older USB cable types can’t? (A lot more but it also depends on the cable). Can a USB C cable damage hardware? (Potentially). USB C can be tricky but much of the confusion is hopefully cleared up in the following pages.

Note: This guide has been revised as the USB Implementor Forum (USB-IF) has made changes over the last few years. You may find products with older labeling. If you are looking for the latest, look under the latest date, which as of the last edit of this guide is January, 2025.

Current Speed Labeling: 2025

The current labeling provides a number specifying the maximum speed the USB port may provide data.

Source: PCWorld, An updated USB logo will now mark the fastest docking stations, January 9, 2025

USB-C ports typically to date have gone unlabeled on computers, so you can’t be sure whether the USB-C port is an older 10Gbps port or a more modern USB4 or Thunderbolt port. (Thunderbolt 4 and USB4v2 are essentially identical, though Intel has its own certification process. Thunderbolt ports aren’t identified by speed, either.) USB-IF representatives believe Dell would begin identifying its ports like the primary image above.

Current Power Delivery (PD) Labeling: 2025

USB power delivery is becoming more common. Higher wattages, typically 100W to 240W are used to power devices like laptops and tablets with mobile devices using less wattage.

The following is a table showing the labeling for speed and wattage to be used for modern (2025 and later) products (click the image to enlarge):

The updated USB logos will also apply to cables. Jeff Ravencraft, president of the USB-IF, said that was done to clearly communicate the only things consumers cared about: what data speeds the cable supported and how much power it could pass between two devices.

Previous Labeling 2021:

In 2021, in an attempt to simplify the 2019 labeling scheme, the USB-IF Announced New Certified USB Type-C® Cable Power Rating Logos.

Note for the latest labeling, see the information under 2025.

Below is the 2021 chart.

Previous Labeling: 2019

In 2019, USB C the connector was used for USB 3, 3.1 Gen 1, 3.1 Gen 2, and Thunderbolt. Confusing, yes! The chart below sorted out some of the differences and may help with older product labeling and packaging. This nomenclature is generally outdated. 

Note for the latest labeling, see the information under 2025.

Below is the 2019 chart: (Click the image to enlarge)

USB C Cables and Hubs on the Market

These three items will fill most USB C related cable needs. Additionally, all of the following parts have the required USB C specifications and certifications including implemented safeguards for protecting cables and ports.

"Full-featured" USB C to USB C cable

This cable can be used for high power (up to 240W) charging of USB C devices as well as 40Gbs data transfer. It is rated for USB C video at 8K@60Hz or 4K@144Hz.

It uses the current USB-IF markings for a maximum of 240W and 40Gbps.

Thunderbolt 4 USB C Cable

This cable can be used for DisplayPort. Which means it can be used with other monitors as display receptacles. Additionally it contains all the same features the above "Full-featured" USB C cable has.

USB C Adapter Hub

The current downside of USB C is that, quite often, newer computers have only USB C ports. This means with older cables and devices you'll often need an adapter to connect to the USB ports. This adapter hub is great for those situations.

This is one of many listed in January, 2025. It's labeled with the old terminology (USB 3.2 Gen 2) and the newer logo (10 megabit). If you need higher speeds, look for that particular speed. In general, the price goes up with higher speed and with power delivery capabilities.

USB C refers solely the shape of a 24 pin connector which can be either a plug or receptacle. The connector has more pins than past USB shapes (like A and micro B) so it can charge devices and transfer your data incredibly quickly. The main purpose that USB C was created for was to do away with all the various cables and adapters to make a more universal solution for both charging and data transfer.

What is it not?

As mentioned earlier, USB C refers to the shape of a 24 pin connector. Just because a cable is USB C doesn’t mean it supports a specific power, transfer speed or protocol. For example, if a cable is USB C it could be USB 3.1 (fast data transfer), 2.0 (slower data transfer) or a different specification. 

How is it different from other USB cables?

• Backwards compatibility. Most older cables had a host side (USB B) and a device side (Micro B). USB C has dual role and is reversible. This means it can transfer power and data both ways.
• Some cables can transfer large amounts of wattage to power monitors or laptops.
• USB C can operate in alternate modes such as DisplayPort, Thunderbolt, HDMI or USB 3.1.
• The cable has a great interoperability, meaning it is highly supported by many well trusted organizations and is becoming a common feature for many devices.

The USB C advantage

What can USB C do?

A USB C cable has the potential to hold some or more of these features:

• Device charging
• Monitor and laptop power
• Fast data transfer - up to 80 Gbps 
• Audio support
• HDMI - see this hdmi.org page
• DisplayPort - see this displayport.org page
• MHL (Mobile High-Definition) - see a good explanation on Wikipedia
• Thunderbolt 3 and 4 - see this Digital Trends article

Again, these features are cable specific, meaning any given USB C cable may not have some of these features. On the other hand, the vast majority of cables can transfer data and charge devices.

The next section will cover the many different USB C cable types and how to select a cable to use for specific features. 

USB C cables can have variations in speed, power, and protocol capabilities.

Additionally there are different length requirements to watch out for. When in doubt, buy cables from the device manufacturer. You can also buy USB C cables from Adafruit as we have specific cables for specific needs that are all tested and researched.

E-Marker Chips Inside Cables

All Type-C cables except the minimal combination of USB 2.0 and only 3 A must contain E-Marker chips that identify the cable and its capabilities via the USB PD protocol. This identification data includes information about product/vendor, cable connectors, USB signalling protocol (2.0, Gen speed rating , Gen 2), passive/active construction, use of V_CONN power, available V_BUS current, latency, RX/TX directionality, SOP controller mode, and hardware/firmware version. It also can include further vendor-defined messages (VDM) that detail support for Alt modes or vendor specific functionality outside of the USB standards.

An interesting video on E-Marker chips: https://www.youtube.com/watch?v=PqR_AkXQp0Q

See the next page for a sample device that can read E-Marker chips.

Speed

A USB C cable with 3.1 Gen 2 capabilities vs one with 2.0 can mean a vast difference in data transfer. For example, two cable types transferring the same HD movie can take vastly different times:

• 3.1 Gen 2 takes 5 seconds at 10 Gbps
• 2.0 takes 1.7 min at 480 MBps

USB C cables run at different speeds measured in bits per second. These include:

• USB 2.0 (2001)
  • 480 Mbps (megabits per second)
• USB 3.0 (2011)
  • 5 Gbps (gigabits per second)
• USB 3.1 Gen 1 (2014)
  • 5 Gbps
• USB 3.1 Gen 2
  • 10 Gbps
  • *Note USB 3.1 gen 4 in store?”
• USB 3.2 (2017)
  • See Wikipedia for a breakdown.
• USB4 (2019)
  • Should not be labeled USB 4.0
  • Based on the Thunderbolt 3 protocol but devices may or may not be Thunderbolt 3 compatible
  • See more on Wikipedia.

If you run across the term “Full-featured” this a reference to speed and typically means USB 3.1 Gen 2.

Going forward, the USB-IF, as of 2025, recommends labeling ports and cables by their speed, rather than the standard they support:

USB Power Delivery (abbreviated USB-PD) was defined in 2012 to provide direct current (DC) voltage and current (power) to devices beyond the previous USB 2 specifications. 

Every normal USB-C cable must support at least 3 amps of current and up to 20 volts for up to 60 watts of power according to the USB PD specification. Cables are also allowed to support up to 5 A (with 20 V limit up to 100 W of power). However, the 20 V limit for 5 A cables has been deprecated in favor of 50 V. The combination of higher voltage support and 5 A current support is called EPR and allows for up to 240 W (48 V, 5 A) of power according to the USB PD specification.

For cables with up to 3A and 5A delivery, they can be used for

• Charging USB type C enabled devices such as cell phones and tablets. 
• Transferring photos and music between devices.

The biggest difference between 3A and 5A cables is 5A cables can generally power laptops and monitors while 3A cables cannot. 

The following is a table showing the labeling for speed and wattage to be used for modern (2025 and later) products (click the image to enlarge):

Updated USB logos will also apply to cables. Jeff Ravencraft, president of the USB-IF, said that was done to clearly communicate the only things consumers cared about: what data speeds the cable supported and how much power it could pass between two devices.

Check Wikipedia for compatibility issues.

Measuring Power Delivery

The ChargerLAB Power-Z KM003C Portable USB-C Fast Charging Tester PD3.1 QC5.0 Digital Voltmeter & Ammeter Power Bank Tester has been held to high regard as to showing voltage, current, and power and the ability to read E-Marker chips. The community states to buy from ChargerLAB/Amazon/known distributors as there are knockoffs. This is not an endorsement, just noting what has been stated online.

Different USB C cables may support different protocols, or ways of transferring data, such as MHL, HDMI, Thunderbolt 3/4/5 and DisplayPort. In relation to USB C, these protocols are called alternate modes. Having support for one protocol type may give support for another but this is not generally the case. 

MHL (Mobile High-Definition) 

• Connects smart phones to TVs.
• Allows MHL-enabled source and display devices to be connected through a USB Type C port.
• Look for MHL support on product page where you are ordering from to ensure MHL is supported.

HDMI

• Allows HDMI-enabled video sources with a USB C connector to directly connect to standard HDMI display devices without requiring an adapter.
• The HDMI Alternate Mode for USB-C allows HDMI-enabled sources with a USB-C connector to directly connect to standard HDMI display devices, without requiring an adapter. The standard was released in September 2016, and supports all HDMI 1.4b features such as video resolutions up to Ultra HD 30 Hz and CEC. Previously, the similar DisplayPort Alternate Mode could be used to connect to HDMI displays from USB type-C sources, but where in that case active adapters were required to convert from DisplayPort to HDMI, HDMI Alternate Mode connects to the display natively.
• More on Wikipedia

Thunderbolt (3, 4, and 5)

• Thunderbolt combines PCI Express (PCIe) and DisplayPort (DP) into two serial signals, and additionally provides DC power via a single cable.
• Typically used for monitors and 4K support. This gives a large speed boost when transferring data at 40 Gbps or more.
• Can require active cables for higher performance, if over 0.5 meters. 
• Thunderbolt 3 cables also support the DisplayPort protocol.
• Thunderbolt 4 was released in July 2020. The key differences between Thunderbolt 4 and Thunderbolt 3 are a minimum bandwidth requirement of 32 Gbit/s for PCIe link and support for dual 4K displays (DisplayPort 1.4).
• On September 12, 2023, Intel previewed Thunderbolt 5 (codenamed Barlow Ridge), aligned to the USB Implementers Forum's (USB-IF) USB4 2.0 specification. It provides symmetric bandwidth of 80 Gbit/s, e.g. for mass-storage devices, double that of Thunderbolt 4, and unidirectional bandwidth of 120 Gbit/s for displays (three times that of Thunderbolt 3 and 4), supporting dual 8K displays at 60 Hz.

DisplayPort

• Another type of digital display interface, backwards compatible with HDMI/DVI/VGA.
• Look for DisplayPort support in product descriptions.

• Currently, DisplayPort is the most widely implemented alternate mode, and is used to provide video output on devices that do not have standard-size DisplayPort or HDMI ports, such as smartphones, tablets, and laptops. A USB-C multiport adapter converts the device's native video stream to DisplayPort/HDMI/VGA, allowing it to be displayed on an external display, such as a television set or computer monitor.

  Examples of devices that support DisplayPort Alternate Mode over USB-C include: MacBook, Chromebook Pixel, Surface Book 2, Samsung Galaxy Tab S4, iPad Pro (3rd generation), iPhone 15/15 Pro, HTC 10/U Ultra/U11/U12+, Huawei Mate 10/20/30, LG V20/V30/V40*/V50, OnePlus 7 and newer, ROG Phone, Samsung Galaxy S8 and newer, Nintendo Switch, Sony Xperia 1/5 etc.

• More on Wikipedia.

In general, the faster the speed of a USB cable, the shorter it should be due to the electrical characteristics inherent to high speed data transfer.

Here are the different passive cable speeds and corresponding suggested lengths (reference):

USB 1.1

• Up to 5 meters

USB 2.0

• Up to 5 meters.

USB 3.1 Gen 1

• Up to 3 meters.

USB 3.1 Gen 2

• Up to 0.8 meter.

USB4

• Up to 0.8 meter.

Thunderbolt Cables

Thunderbolt maximum cable lengths vary per the standard and whether passive or active. It is best to label the cable you get with a peripheral and always ensure that cable is used with its peripheral.

Thunderbolt 3 cables

• If the cable is over half a meter, it needs to be a special active cable, meaning there are a bit of electronics inside to help things out.
• If 0.8 m or under, can be passive. The only thing under the rubber sheathing is copper wire.
• For more details, check the product pages of the cables you are considering.

Thunderbolt 4 Cables

Copper versions of Thunderbolt 4 cables offer full 40 Gbit/s speed and backward compatibility with all versions of USB (up to USB4), DisplayPort Alternate Mode (DP 1.4 HBR3), and Thunderbolt 3. Released in early 2021, they are also all to be available in three specified lengths: 0.2 m (0.66 ft), 0.8 m (2.6 ft), and 2 m (6.6 ft) – with many companies initially offering 0.8 m (2.6 ft) lengths. Copper Thunderbolt 4 cables up to 1 m (3.3 ft) are passive cables, while longer cables must integrate active signal conditioning circuitry.

Thunderbolt 5 Cables

Passive cable is available in 3 different lengths: 1 foot, 1.6 feet and 3.3 feet, supporting up to 80 Gbps of bi-directional data transfer and up to 120 Gbps of video bandwidth. (Reference)

Extending USB Cable Length

While exceeding the maximum lengths for USB cables can lead to performance issues, there are scenarios where longer reach is necessary.

Active Extension Cables

Active extension cables are designed specifically to overcome the length limitations of standard USB cables. These cables contain built-in electronics that amplify the signal, enabling longer cable lengths without significant loss of data transfer speed or signal integrity. 

USB 2.0

• Up to 30 meters.

USB 3.0 and 3.1

• Up to 18 meters

USB 3.2 and USB4

• Up to 3 meters

USB Extenders

USB extenders offer another robust solution for extending USB cable length, particularly for very long distances. USB extenders typically convert the USB signal into another form, such as Ethernet, which can travel over much longer distances without degradation. The signal is then converted back to USB at the receiving end. There are two main types of USB extenders:

• USB over Ethernet Extenders:These devices use standard Ethernet cables (Cat5e, Cat6) to extend USB connections up to 100 meters (approximately 328 feet). They consist of a transmitter unit that connects to the source device and a receiver unit that connects to the destination device. This method is ideal for large office spaces or industrial environments.
• Wireless USB Extenders:These extenders use wireless technology to transmit USB signals over the air. While they typically offer shorter maximum distances than Ethernet-based extenders, they provide the advantage of eliminating physical cables, offering flexibility in device placement.

Practical Considerations

• Keep cable lengths as short as necessary
• Use high-quality cables
• Use properly marked cables if available
• Keep cables away from electromagnetic interference
• Replace damaged or frayed cables

See Wikipedia for more in-depth cable information and potential issues.

Many new laptops, such as the Macbook Pro, have only USB C ports. If you’re trying to connect any non-USB C device like USB 3.1, HDMI or Thunderbolt, you’ll need an adapter.

Legacy Adapters

Connecting an older device to a host with a USB C receptacle requires a cable or adapter with a USB A or USB B plug or receptacle at one end and a USB C plug at the other. Legacy adapters (i.e. adapters with a USB A or USB B plug) with a USB C receptacle are "not defined or allowed" by the specification since they can create "many invalid and potentially unsafe" cable combinations.

Adafruit sells a USB plug to USB A socket for legacy devices. These adapters don't magically give you USB C speeds into a USB 2.x device, and they won't give you the power negotiation capabilities because those pins aren't available on type A connectors. So it's strictly for devices that use 5V and up to perhaps 2.5A.

And for something bigger:

Audio Adapter Accessory Mode

A device with a USB C port may support analog headsets through an audio adapter with a 3.5 mm jack, providing four standard analog audio connections (Left, Right, Microphone, and Ground). The audio adapter may optionally include a USB C charge-through port to allow 500 mA device charging. 

A great number of these are marketed for cell/mobile phones. If you need one for a single board computer, be careful of the labeling. Most single board computer adapters are USB A. 

Also beware such adapters will not add audio capability to a microcontroller. Look for add-ons that are likely not USB specifically tailored to the microcontroller you are working with as there are several audio interface methods (DAC, I2S) to consider.

See Wikipedia for additional information.

Alternate Modes

Alternate Mode hosts and sinks can be connected with either regular full-featured USB C cables, or converter cables/adapters:

USB 3.1 Type C to Type C full-featured cable

• DisplayPort, MHL, HDMI and Thunderbolt Alternate Mode USB C ports can be interconnected with standard passive full-featured USB Type C cables. These cables are only marked with standard "trident" SuperSpeed USB logo (for Gen 1 cables) or the SuperSpeed+ USB 10 Gbit/s logo (for Gen 2 cables) on both ends. Cable length should be 2.0 m or less for Gen 1 and 1.0 m or less for Gen 2

Thunderbolt Type C to Type C active cable

• Thunderbolt 3 Alternate Mode with cables longer than 0.5 m requires active USB C cables that are certified and electronically marked for high-speed Thunderbolt 3 transmission, similarly to high-power 5 A cables. These cables are marked with a Thunderbolt logo on both ends. They do not support USB 3 backwards compatibility, only USB 2 or Thunderbolt. Cables can be marked for both Thunderbolt and 5 A power delivery at the same time.

USB 3.1 Type C adapter cable (plug) or adapter (socket)

• These cables/adapters contain a valid DisplayPort, HDMI, or MHL plug/socket marked with the logo of the required Alternate Mode, and a USB-C plug with a "trident" SuperSpeed 10 Gbit/s logo on the other end. Cable length should be up to 0.15 meters.
• Active cables or adapters contain powered ICs to amplify/equalize the signal for extended length cables, or to perform active protocol conversion. The adapters for video Alt Modes may allow conversion from native video stream to other video interface standards (e.g., DisplayPort, HDMI, VGA or DVI).

Power Caution

The amount of power that cables may deliver can differ for different devices. For example: If you use a cable that draws more power than a port can handle, you could harm the port.

Cables are supposed to contain safeguards. Sometimes manufacturers cut corners to reduce cost and don’t follow standards, including the implementation of these safeguards.

Buying Cables Online

• Read reviews from wherever you are buying your cables. Make sure people are using for the same purposes as you (transferring data, streaming video to a TV/monitor, etc).

Connecting to Monitors and laptops

• Use a specific cable for power and data transfer (usually marked with a DisplayPort or Thunderbolt symbol)
• Always double check cable capabilities before using to power laptops or monitors

Identifying Your Cable

If you are still unsure of what kind of USB C cable you have after looking for product specifications and checking comments on the product page, look for one of the below symbols on the cable to identify the cable type. 

Even if you are correctly able to identify the cable, never use a cable to power a laptop or monitor unless you are certain the cable supports 5A and you have double checked online resources about the specific cable you are using.

F.A.Q

Label Your Cables!

• While cables do have individual markings, they should be more obvious and they are not.

Power

• If you plan on using an unknown cable for charging be careful, especially to when charging a computer.
• *NEVER USE A 3A USB C CABLE TO POWER A LAPTOP OR MONITOR*
• Always double check a cable’s capabilities before using to power laptops or monitors
• If you are just performing data transfer, you will typically be ok.

Display

• Some cables are meant for display receptacles only. 
• These are generally Thunderbolt 3 / 4 / 5 cables and are marked with the Thunderbolt logo.

Buying Cables

• Try to use the cable that came with the device when you purchased it. When in doubt, buy cables from the device manufacturer. 
• Read reviews wherever you are buying cables from and make sure people are using for what you want to (read their comments)
• Cables from less-than-reputable sources may have cut corners. In doing that, they may have removed features which keep you safe.
• Look for modern labeling which shows a cable is certified for a specific use.

When in USB C doubt, check the graphics out!

By taking these precautions, you save yourself stress and avoid damaging your hardware and ports. Good luck with your connector adventures!