USB Transfer Speed Test
Benchmark your USB device transfer performance and compare with standard USB 2.0/3.0/3.1 speed specifications.
This test benchmarks USB device throughput via the WebUSB API by transferring data blocks and measuring effective transfer speed, then comparing results against official USB specification maximums.
Real-world USB 3.0 delivers approximately 400 MB/s (3.2 Gbps) of its 5 Gbps theoretical maximum, while USB 2.0 typically achieves 35 MB/s of its 480 Mbps spec due to protocol overhead.
What Do Your Results Mean?
| Result | Range | Meaning |
|---|---|---|
| Good | Within 60-80% of USB standard's theoretical maximum | Your USB connection is performing as expected. USB 2.0 at 25-35 MB/s, USB 3.0 at 300-400 MB/s, or USB 3.1 Gen 2 at 700-900 MB/s indicates a healthy connection. |
| Warning | 30-60% of theoretical maximum | Speed is below typical. Check if the cable or port is limiting performance — a USB 3.0 device in a USB 2.0 port will cap at 35 MB/s. Also check for background transfers consuming bandwidth. |
| Bad | Below 30% of theoretical maximum or matching a lower USB standard | The device is likely connected to a lower-spec port or using an incompatible cable. Verify port type (blue = USB 3.0), try a different cable, and check USB controller drivers. |
Common Issues and How to Fix Them
Speed test shows USB 2.0 speeds on a USB 3.0 device
Check that both the port and cable support USB 3.0. USB 3.0 ports have a blue interior. USB 3.0 cables are thicker and have 9 pins. Avoid hubs that may downgrade the connection.
WebUSB cannot access the storage device
Mass storage devices (flash drives, external HDDs) are typically claimed by the OS file system driver and unavailable to WebUSB. This test works with devices that expose a WebUSB-compatible interface.
Speed results are inconsistent between runs
Close other applications transferring data, avoid using a USB hub, and ensure the device isn't thermal throttling. SSDs in enclosures may slow down after sustained transfers due to heat.