This USB speed test measures how fast a flash drive, external SSD or USB hard drive really reads and writes. You pick the drive in a standard folder dialog, and the tester writes a set of test files to it, reads them back, checks every block came back unchanged, and deletes them. Along the way it times hundreds of small 4 KB files, the kind of load that makes cheap drives crawl. It runs in Chrome, Edge and Opera on Windows, macOS, Linux and ChromeOS. Other browsers and phones can still measure their own storage with the This device button.
How to test USB speed
- Plug the drive into a port on the computer itself, not a hub or a monitor's USB port, so the result shows the drive and not the hub.
- Press Choose and pick the USB drive in the folder dialog. If the browser refuses the top of the drive, make a new folder on it and pick that. Allow editing when the browser asks.
- Pick a size. 256 MB is quick. 1 GB or 4 GB gives steadier figures and shows whether the speed drops once the drive's fast cache fills.
- Press Start test and keep the drive connected. The graph draws write speed in yellow.
- When writing ends, eject the drive, unplug it and plug it back in. The read starts by itself and draws in green.
- Name the run, for example "front port", then repeat on another port to compare them in Your recent runs. Copy results gives you a summary for a support ticket or a review.
What the results mean
| Readout | What it measures | Typical USB 3 flash drive |
|---|---|---|
| Write | Speed saving large files, in MB/s | 20 to 200 MB/s |
| Read | Speed opening large files, in MB/s | 100 to 400 MB/s |
| Small file writes | 4 KB files saved per second | 20 to 200 per second |
| Small file reads | 4 KB files opened per second | 200 to 2,000 per second |
| Copy a 4 GB file | Time to copy one 4 GB file onto the drive | Under 2 minutes |
Speeds are in megabytes per second, the same unit drive makers use. Small file figures include the browser's own work for each file, so compare them between drives and ports rather than with figures from other tools.
Real world USB speeds
The number on the box is the link speed in bits. Real transfers lose part of it to encoding and protocol overhead, so a drive never reaches the headline figure.
| Connection | Link speed | Best real transfers | Port hints |
|---|---|---|---|
| USB 2.0 | 480 Mbps | 35 to 42 MB/s | Black or white USB-A |
| USB 3.2 Gen 1 (USB 3.0) | 5 Gbps | 400 to 450 MB/s | Blue USB-A, "SS" or "5Gbps" logo |
| USB 3.2 Gen 2 | 10 Gbps | 900 to 1,050 MB/s | Teal or red USB-A, "SS 10" or "10Gbps" logo |
| USB 3.2 Gen 2x2 | 20 Gbps | 1,800 to 2,000 MB/s | USB-C only |
| USB4 and Thunderbolt 3 or 4 | 40 Gbps | 2,800 to 3,800 MB/s | USB-C with a 40 or lightning bolt logo |
A flash drive usually sits well below its link. Many "USB 3.0" sticks write at 10 to 30 MB/s, because the limit is the memory chips, not the cable.
The drive is stuck near 40 MB/s
A read that tops out between 30 and 42 MB/s is the USB 2.0 ceiling. A USB 3 drive should beat it easily, so something in the chain is running at USB 2.0:
- The port. Many laptops and front panels mix USB 2.0 and USB 3 ports. Try a blue port or one marked SS. When a fast drive sits in a slow port, Windows sometimes says it "can transfer information faster if you connect it to a Super-Speed USB 3.0 port".
- The cable. USB-C cables that come with phones and chargers often carry only USB 2.0 data. Use the cable that came with the drive or one rated 5, 10 or 20 Gbps.
- A hub or dock. Plug straight into the computer and test again.
- Drivers. On older Windows PCs, install the chipset or USB 3 driver from the computer maker.
To see the link speed directly: on a Mac open System Information, then USB, and read the Speed line. On Linux, lsusb -t shows 480M for USB 2.0 and 5000M or more for USB 3. On Windows, the free UsbTreeView tool lists each port's speed.
Write speed is far below the box
Box figures are usually the read speed, measured in the maker's own best case. Writes are often a quarter of it. If your result is low compared with reviews of the same model, check these:
- The graph drops partway through. Fast drives write to a small, quick cache first. When it fills, speed falls to what the memory can sustain. That lower level is what you get when copying big files.
- The drive is nearly full. Flash drives slow down with little free space. Test with at least a few GB free.
- The drive is hot. Small metal sticks throttle when warm. Let it cool and test again.
- The drive is fake. Very low, uneven write speed is a common sign of a counterfeit stick. Check it with the fake flash drive test.
The read result looks impossibly fast
A flash drive that "reads" at 2,000 MB/s or more is not showing its own speed. The computer kept a copy of the test files in memory and served them from there. The tester marks such a figure in orange. Turn on Replug before reading so the drive is unplugged between writing and reading, which clears that copy.
Some data did not match
Every 4 KB block the tester writes carries its own number, and the read checks each one. A mismatch means the drive returned the wrong data. If you pulled the drive without ejecting it, run the test again. If it happens again, the drive is failing or reports more space than it has. Copy your files off it and run the full capacity check. If Windows also shows errors when you plug it in, the usb device not recognized guide covers ports, power and drivers.
Testing SD cards and SSDs
Memory cards depend on the card reader as much as the card. The sd card speed test uses the same engine and checks the result against speed classes such as U3, V30 and V60. For an internal drive, the hard drive speed test measures this computer's own SSD or hard drive through the browser's private storage.
What a browser speed test cannot measure
The test works through normal files, the way your programs do, so it shows the speed you will get when copying files. It cannot reach the drive below the file system, so it does not run the queue depth tests of benchmark tools. On very fast drives, above about 2,000 MB/s, the browser's own work becomes the limit. Chrome and Edge also check each saved file, which can trim the write figure on fast external SSDs.
For full benchmarks, use CrystalDiskMark on Windows, Blackmagic Disk Speed Test or AmorphousDiskMark on a Mac, or GNOME Disks (Benchmark Disk) on Linux. On Linux you can also time a write with dd if=/dev/zero of=/media/you/DRIVE/test.img bs=1M count=1024 oflag=direct status=progress, then read the file back after unplugging the drive.
USB speed test questions
Is this USB speed test safe for the files on my drive?
Yes. The test only creates its own files, named drive-speed-test, in the folder you choose. It never opens, changes or deletes anything else, and it removes its own files when it finishes or when you press Stop. Nothing is uploaded.
Why is my USB 3.0 flash drive so slow?
The three usual causes are a USB 2.0 port or hub, a USB-C cable that only carries USB 2.0, and a drive that is simply slow at writing. If the read stays near 40 MB/s, it is the port or cable. If the read is fast but the write is under 20 MB/s, it is the drive itself. Cheap flash drives often write at 10 to 30 MB/s even on USB 3.
What is a good USB flash drive speed?
On a USB 3 port, a decent flash drive reads at 100 MB/s or more and writes at 30 MB/s or more. Fast models read at 300 to 400 MB/s and write at 150 MB/s or more. An external SSD on a 10 Gbps port reaches about 1,000 MB/s both ways.
How do I check USB speed on Windows 11 without software?
Open Terminal as administrator and run winsat disk -drive E, replacing E with your drive letter. It prints sequential read and write and random read figures in MB/s. This page gives you the same large file figures without the command line.
Why is the read speed so much higher before I unplug the drive?
Your computer keeps recently written data in memory. Reading it back right away measures that memory, which can show thousands of MB/s. Unplugging the drive clears that copy, so the read after replugging comes from the drive itself. Leave Replug before reading on for honest results.
Can I test a USB drive on an Android phone or iPhone?
Not on this page: testing a USB drive here needs Chrome, Edge or Opera on a computer. On a phone, the This device button still measures the phone's own storage, and a storage benchmark app can test a drive connected with a USB OTG adapter.