How to check USB 3 speed with a card reader

You switched card readers and now copying photos feels slower. The reader may be using a USB 2 connection instead of USB 3, but a slow card, adapter, hub, or busy computer can cause the same symptom.

The USB & SD Speed Test measures actual read and write speeds. It cannot report the USB link rate directly, but the results can show whether the new setup is behaving like a slower connection.

Test the card reader's speed

1. Open the USB & SD Speed Test and follow its prompts to select the memory card or USB drive.
2. Use the same card, computer, and files or test conditions you used with the old reader. Back up important files before a test that writes data.
3. Run both the read and write measurements. Note the results in MB/s, or megabytes per second.
4. Repeat the test with the reader connected directly to a USB port on the computer, not through a hub or dock.
5. If possible, repeat with the old reader in the same port. Close large downloads, file copies, and other tasks first, since they can affect the result.

For a useful comparison, change only one part at a time. If you switch the card, port, cable, and reader together, the results will not show which change mattered. For more on comparing readers, see how to test storage speed after replacing a card reader.

What the result means

Speed stays around 20 to 40 MB/s

This range can be a clue that the reader is connected through USB 2, especially if the same card was much faster in another setup. It is not proof: some memory cards write slowly, and their read speed can also be limited by the card itself.

Read speed is much higher than write speed

That difference is common. Many cards read data faster than they can save it. Compare the same direction across readers: a faster read result does not mean the card can write at that speed.

The new reader is much slower in both directions

The connection path is a likely cause if the same card and computer were used. Check whether the reader is in a USB 2 port, attached through a slower hub, or connected with an adapter or cable that limits it. The speed test measures the whole path, not just the reader.

The new reader is faster, but not dramatically

The card may be the limit. USB 3 at 5 Gbps has a theoretical rate of 625 MB/s before overhead, but a card reader and card usually transfer far less. For example, a UHS-I SD card has a theoretical bus rate of 104 MB/s, and real results are lower.

Results vary a lot between runs

Background activity, a nearly full card, heat, and file-system activity can affect transfer speeds. Repeat the test under similar conditions before deciding that the reader or card is faulty.

How to fix a slow connection

1. Try another port. Connect the reader directly to a port marked with a SuperSpeed symbol or a blue insert, if present. Color and symbols are not universal, so check the computer's documentation if you are unsure which ports support USB 3.
2. Remove the hub or adapter. Test the reader directly on the computer. A hub, dock, extension cable, or adapter may support USB 2 even when the computer has USB 3 ports.
3. Check the reader and cable specifications. A USB-C plug does not guarantee USB 3 speed. Confirm that the reader and any detachable cable support SuperSpeed, which commonly means 5 Gbps or faster.
4. Check what the computer reports. On macOS, open Apple menu › About This Mac › More Info › System Report › USB and inspect the reader's connection details. On Windows 11, open Device Manager › Universal Serial Bus controllers and check for USB 3 host controllers or hubs. Their presence confirms USB 3 support on the computer, not that this reader negotiated a USB 3 link; Windows does not show the negotiated rate consistently in this view.
5. Reconnect and retest. Unplug the reader, wait a few seconds, and reconnect it directly to the chosen port. Then test again with the same card. Do not remove the card while data is being written.

When the reader or card may be faulty

Test the same card in both readers and, if available, test a second card in the new reader. If only one card is slow, the card is more likely to be the limit or to have a problem. If every card is slow in the new reader, but performs normally in the old one on the same port, the new reader or its cable is a stronger suspect.

Back up the card before more write tests if it contains important files. If the reader remains slow across different cards and known USB 3 ports, check its warranty or replace it. A browser speed test can compare transfer behavior, but it cannot certify the reader's electronics or prove its advertised USB version.

Why a speed test cannot show negotiation by itself

USB link speed describes the connection between the computer and reader. The card has its own speed limit, and the reader also has a maximum rate. The test sees only the final transfer rate after all of those limits, plus the browser and computer, have affected the result. A low number can suggest a USB 2 fallback, but it cannot identify the cause on its own.

Run the test on the card and reader you want to check, and keep the same setup when comparing results.