USB Drive Speed Test
How fast is your flash drive or memory card really? Pick a folder on the drive and this test writes a temporary file, reads it back and reports the sequential write and read speed in MB/s, then deletes the file.
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Choose a folder on your USB flash drive, SD card or external disk. The test writes a temporary file there, reads it back and deletes it.
Nothing is uploaded: all reading and writing happens between this page and the folder you pick.
| Test | Data | Time | Speed |
|---|---|---|---|
| Results appear here after a test. | |||
Make sure the drive has free space at least the size of the test file. Temporary files are named ftc-speedtest-… and are deleted at the end, even if you stop the test.
How to use the USB Drive Speed Test
- Plug in the drive and make sure it has free space at least as large as the test file.
- Choose the test file size. 256 MB is a good default; use 1 GB for drives with a large write cache.
- Press Choose drive and start test and select any folder on the drive, then allow the browser to edit files there.
- Wait for the write and read phases. The chart shows the speed of each block as it is written and read.
- Read the results. Compare the MB/s with the advertised speed and the reference table below, then copy the results if needed.
What the speed test measures
- Sequential write: one large file written in blocks (4 MB by default). Speed = file size ÷ time from the first block until the file is closed, which is when the browser commits it to the drive. This is the speed you see when copying a big video or ISO file to the drive.
- Sequential read: the same file read back from start to end. The tool checks that every byte arrived.
- Small files: 200 separate 32 KB files written and read. Flash drives are much slower with many small files because each file needs its own directory and allocation updates, so this reflects copying photo folders or documents.
Speeds use binary megabytes: 1 MB/s = 1,048,576 bytes per second. Drive makers usually quote decimal MB (1,000,000 bytes), so a drive rated 100 MB/s shows about 95 MB/s here even at full speed.
Typical speeds by drive and interface
| Drive or connection | Typical read | Typical write |
|---|---|---|
| USB 2.0 flash drive (480 Mbit/s bus) | 20 to 35 MB/s | 5 to 15 MB/s |
| Budget USB 3.0 / 3.2 Gen 1 flash drive | 80 to 150 MB/s | 15 to 40 MB/s |
| Premium USB 3.2 flash drive | 200 to 420 MB/s | 100 to 380 MB/s |
| SD card Class 10 / UHS-I U1 | up to about 90 MB/s | 10 MB/s minimum |
| SD card UHS-I U3 / V30 | up to about 100 MB/s | 30 MB/s minimum |
| SD card UHS-II V60 / V90 | 150 to 300 MB/s | 60 / 90 MB/s minimum |
| External hard drive (USB 3.0) | 100 to 200 MB/s | 100 to 180 MB/s |
| Portable SSD (USB 3.2 Gen 2, 10 Gbit/s) | 900 to 1,050 MB/s | 800 to 1,000 MB/s |
SD card speed classes (Class 10, U1, U3, V30, V60, V90) are guaranteed minimum sustained write speeds for video recording, defined by the SD Association.
Tips for accurate results
- Use a direct USB 3 port (often blue or marked SS) instead of a hub, and a fast card reader for SD cards. The slowest link sets the speed.
- Pick a larger file for big drives. Many drives have a fast cache that hides the slower sustained speed; 1 GB shows when it runs out, visible as a drop in the chart.
- Close other programs that might be copying to the drive, and avoid antivirus scans during the test.
- Re-plug before a read test if you want a cache-free read figure, then run the test again.
- Nearly full drives are slower. Flash memory needs free blocks to write quickly, so test with plenty of free space.
Frequently asked questions
How does a browser test USB drive speed?
Chrome, Edge and other Chromium browsers support the File System Access API, which lets a page write files to a folder you choose. The test writes a file of random data in large blocks, measures the time until the data is committed to the drive, then reads the file back and measures that time. Speed = data size ÷ time, shown in MB/s (1 MB = 1,048,576 bytes).
Is it safe for the files on my drive?
Yes. The test only creates its own temporary files named ftc-speedtest-… in the folder you pick and deletes them at the end. It never reads, changes or deletes your other files, and nothing is uploaded anywhere.
Why is my read speed much higher than expected?
Right after a file is written, the operating system may keep a copy in memory, so reading it back can come from RAM instead of the drive. If the read speed is far above the drive's rating, use a larger test file (512 MB or 1 GB) or rely on the write speed. Safely removing and reconnecting the drive clears that cache.
Why is the write speed lower than the speed on the package?
Advertised speeds are usually the maximum read speed under ideal conditions. Write speeds of flash drives and cards are often 3 to 10 times lower, can drop once an internal cache fills, and are limited by the port: a USB 3.0 drive in a USB 2.0 port or a slow card reader tops out at about 30 to 40 MB/s.
Which browsers support the USB speed test?
Chrome, Edge, Opera, Brave and other Chromium browsers on Windows, macOS, Linux and ChromeOS. Firefox and Safari do not support choosing a writable folder yet, and mobile browsers cannot access USB drives this way. On those, you can still test the browser's own storage.
Can this test detect a fake or counterfeit flash drive?
It verifies that every byte written is read back, which can catch some faulty drives, but a fake drive usually only fails once you write more than its real capacity. Use the fake flash drive checker to test the full capacity.
What is a good USB flash drive speed?
For a USB 3.x flash drive, around 100 MB/s read and 30 MB/s write or more is decent, and premium drives reach 300 to 400 MB/s. USB 2.0 drives typically read at 20 to 35 MB/s and write at 5 to 15 MB/s. Portable SSDs on USB 3.2 Gen 2 reach about 1,000 MB/s.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.