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USB 4 Speeds vs Thunderbolt: Full Comparison

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USB 4 Speeds vs Thunderbolt: Full Comparison

USB4 and Thunderbolt are often mentioned together, and the short answer is: USB4 can match Thunderbolt speeds, but it doesn’t always. The USB4 specification is based on Thunderbolt 3 technology, so it supports up to 40 Gbps, the same maximum as Thunderbolt 3 and Thunderbolt 4. However, USB4 devices and ports are not required to hit that maximum, and Thunderbolt 4 certification enforces a strict set of features that USB4 does not.

Background: How USB4 and Thunderbolt Are Related

USB4 was introduced by the USB Promoter Group in 2019, and it is built on the Thunderbolt 3 protocol that Intel contributed to the standard. This means the underlying data transfer method is the same, which is why USB4 and Thunderbolt share the same 40 Gbps ceiling. Before USB4, USB 3.x topped out at 20 Gbps, and Thunderbolt 3 was the only consumer interface hitting 40 Gbps.

Thunderbolt 4, released in 2020, is essentially a certification for USB4 devices that guarantees minimum performance and feature requirements. Intel controls the Thunderbolt brand, so a device can only use the Thunderbolt name if it passes Intel’s certification tests. USB4, on the other hand, is an open standard that any manufacturer can implement without certification, which leads to a wide range of actual speeds and capabilities.

How USB4 and Thunderbolt Speeds Compare

The maximum speed for both USB4 and Thunderbolt 4 is 40 Gbps (gigabits per second). That is the theoretical ceiling, and real-world throughput is lower due to encoding overhead and protocol limitations. In practice, you might see around 3,000 MB/s for a fast NVMe SSD over either interface, which is roughly 24 Gbps of actual data.

However, USB4 has a catch: not every USB4 port or cable supports 40 Gbps. The USB4 specification allows for two speed tiers:

  • USB4 Gen 3×2: 40 Gbps (the full Thunderbolt speed)
  • USB4 Gen 2×2: 20 Gbps (half the Thunderbolt speed)

If a laptop has a USB4 port, it might be either tier. Many budget laptops include USB4 Gen 2×2 ports that only reach 20 Gbps, while Thunderbolt 4 ports always operate at 40 Gbps. Additionally, USB4 cables are rated for speed: a USB4 cable marked as 40 Gbps is required for full speed, while a 20 Gbps cable will cap the connection.

Beyond Speed: What Thunderbolt 4 Adds

Thunderbolt 4 is not just about raw speed; it is a certification that mandates a set of features. A Thunderbolt 4 port must support:

  • 40 Gbps data transfer
  • At least one 4K display (or two 4K displays on some systems)
  • PCIe data at 32 Gbps for external GPUs and high-speed storage
  • Power delivery up to 100W for charging laptops
  • Wake from sleep via the port
  • Intel VT-d based DMA protection for security

USB4 ports are not required to meet any of these minimums. A USB4 port might support only a single display, or no display at all, and might not support external GPUs. It might also deliver less power. This is why two devices with the same 40 Gbps USB4 port can behave very differently when you connect a monitor or an eGPU.

How to Check What Your Port Supports

If you want to know whether your USB4 port runs at 40 Gbps or 20 Gbps, look for the logo or the spec sheet. Thunderbolt ports are labeled with a lightning bolt icon, and Thunderbolt 4 cables often have a “4” inside the bolt. USB4 ports are usually labeled with “USB4” and sometimes include the speed, like “USB4 40Gbps” or “USB4 20Gbps.”

On a laptop, you can also check the manufacturer’s specifications online. Look for the exact model’s tech specs page and search for “USB4” or “Thunderbolt 4.” If it says “USB4 40Gbps,” you get full Thunderbolt speed. If it says “USB4 20Gbps,” you are limited to half speed. For desktops, the motherboard manual or the product page will list the port speeds.

Common Misconceptions and Pitfalls

One common misconception is that all USB-C ports are the same. USB-C is just the physical connector shape; it can carry USB 2.0, USB 3.x, USB4, Thunderbolt, or even DisplayPort and power only. Plugging a USB4 device into a plain USB 3.2 port will drop the speed to 10 or 20 Gbps, depending on the port.

Another pitfall is cable quality. A cheap USB-C cable might only support USB 2.0 speeds (480 Mbps), even if both the port and device support USB4. Always check the cable’s rating: it should say “USB4 40Gbps” or “Thunderbolt 4” on the connector or packaging. Using a Thunderbolt 3 cable with a USB4 port usually works at 40 Gbps, but a USB 3.x cable will not.

Also, note that USB4 and Thunderbolt are backward compatible. You can plug a USB 3.x device into a USB4 or Thunderbolt port, and it will work at the lower speed. Similarly, a USB4 device plugged into a Thunderbolt 4 port will work, but only at USB4 speeds, which might be 20 Gbps if the device is a 20 Gbps model.

Which One Should You Choose?

If you are buying a laptop or desktop, the choice between USB4 and Thunderbolt 4 depends on your needs:

  • If you only connect external drives and charge your phone, a USB4 port is fine, even at 20 Gbps.
  • If you plan to use an external GPU, a high-resolution monitor, or a fast NVMe SSD, you want Thunderbolt 4 or USB4 at 40 Gbps.
  • If you need to daisy-chain multiple Thunderbolt devices, Thunderbolt 4 supports up to six devices in a chain, while USB4 does not guarantee daisy-chaining.
  • If you are on a budget, USB4 ports are more common on affordable laptops, but check the speed tier before buying.

For most users, the practical difference between USB4 40 Gbps and Thunderbolt 4 is minimal. Both can handle a single 4K monitor and fast storage. The real gap is between USB4 20 Gbps and Thunderbolt 4, where the latter is twice as fast for data and supports more displays.

Frequently Asked Questions

Is USB4 faster than Thunderbolt 3?

USB4 and Thunderbolt 3 both have a maximum speed of 40 Gbps. However, Thunderbolt 3 is a certified standard with guaranteed minimums, while USB4 may be implemented at 20 Gbps. So a full-speed USB4 port matches Thunderbolt 3, but a lower-tier USB4 port is slower.

Can I use a Thunderbolt 4 cable with a USB4 port?

Yes, Thunderbolt 4 cables are fully compatible with USB4 ports. They will carry USB4 signals at the port’s maximum speed, which is 40 Gbps if the port supports it. The cable itself is rated for 40 Gbps, so it will not be the bottleneck.

Does USB4 support external GPUs?

USB4 can support external GPUs, but it is not guaranteed. The USB4 specification allows for PCIe tunneling, which is required for eGPUs, but a specific USB4 port might not implement it. Thunderbolt 4 requires PCIe support, so it is the safer choice for eGPU use.

Why is my USB4 device only running at 10 Gbps?

If your USB4 device is running at 10 Gbps, it is likely using a USB 3.2 Gen 2 connection instead of USB4. This can happen if the port is actually USB 3.2, the cable is not USB4-rated, or the device itself is not USB4. Check both the port and cable specifications.

Is Thunderbolt 4 the same as USB4 40Gbps?

Thunderbolt 4 is a certification that requires USB4 at 40 Gbps, but it adds extra requirements like PCIe support, 100W power delivery, and DMA protection. A USB4 40Gbps port might not meet those extras, so they are not the same, even though the base speed is identical.

Can I connect a Thunderbolt 3 device to a USB4 port?

Yes, USB4 is backward compatible with Thunderbolt 3. A Thunderbolt 3 device will work in a USB4 port, and it will run at its native speed, which is up to 40 Gbps. The same applies to Thunderbolt 4 devices in USB4 ports, as long as the port supports the required features.

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