USB drive speed test. And a fake capacity check.
Pick a folder on the drive, and the page writes its own folder of test files there, reads every byte back and checks it, then deletes its files. You get write and read speed, and whether everything written survived. A fake drive reports more space than it has and loses data past its real size; the optional full check fills the free space to find where. Chrome and Edge on a computer only.
One check · Minutes to hours
Asks for: A folder on the drive, in Chrome or Edge. It runs in its own window and nothing leaves this page.
In short
USB drive speed test: the answer first
A USB drive speed test writes files to the drive, reads them back and times both. This one runs in Chrome or Edge on a folder you pick, checks every byte it wrote, and with the optional full check fills the free space to find fake capacity: a fake drive loses data past its real size, and the first file that fails shows where.
Reading your result
- Every byte correct
- Everything written read back as written. On a quick test that covers only the amount written; only the full check can rule out a fake drive.
- Data lost past a point
- The drive returned wrong data after a certain amount: consistent with fake capacity or failing flash. Do not trust it beyond that point.
- Write speed falls and stays down
- The drive's fast cache ran out. The speed after the fall is what a large copy will see.
What it measures
Measured here, not assumed.
- Write speed
- Files of up to 256 MiB written in 1 MiB blocks, each timed from opening it to the browser committing it, including generating the data. The figure is the median per file. A lasting fall to under half the early speed is reported as the drive's fast cache running out (our line).
- Every byte, checked
- Each block carries its file number, block number and the run's seed, and data that follows from them, so a block that reads back blank, changed or from the wrong place is caught.
- Read speed
- Each file read back in 1 MiB slices. Until the drive is unplugged and plugged back in, the system may serve this from memory; the page says so and offers to verify again after a replug.
- Full check for fake capacity
- Optional: files until the drive reports it is full, then everything read back. The first file that fails is where the real capacity ends. Slow, and it fills the drive until the page deletes its files.
If it fails
The usual failures, and what fixes each.
- Data did not read back
- Copy off anything you need, then format the drive and run the full check again. If it fails at the same point, the real capacity ends there: return the drive.
- Write speed is far below the box
- Check the port: a USB 2 port or a hub limits the drive whatever it is rated for. Plug into a USB 3 port on the computer itself, not a hub, and run again.
- The browser will not let the page use the folder
- Chrome blocks system folders and the root of some drives. Make a new folder on the drive and choose that.
Where a browser stops
What it cannot tell you.
- The drive's health, controller or flash type. The test goes through the file system, not the raw device.
- Space other files already use. Only the space the test files took is checked.
- Read speed without a replug. The system's cache can make it read far faster than the drive.
- Firefox, Safari and phones. They do not offer the File System Access API, and the page says so.
- The USB port's speed. A slow port or hub limits the result; the page cannot see which port is used.
Privacy
Nothing leaves this page.
The test files are written only inside the folder of its own the page makes on the drive you choose, and that folder is deleted at the end. Nothing else on the drive is read, and nothing is uploaded. The result is not stored anywhere.
Questions
USB drive speed test, answered
- How do I check if a USB drive is fake?
- Fill it and read everything back: a fake drive accepts writes past its real size and returns wrong data for them. Run the full check above; the first file that fails shows where the real capacity ends.
- How do I test a USB drive's speed online?
- Open the test in Chrome or Edge, choose a folder on the drive and an amount, and start. The page writes and reads back its own test files and reports MB/s for each.
- Does the test delete my files?
- No. It only writes inside a folder of its own, named systemcheck-drive-test followed by a code, and deletes that folder at the end. Your files are not read or changed.
- Can I test an SD card?
- Yes, in a card reader the computer shows as a drive. The reader's own speed limits the result.
- Why is the read speed so much faster than the write?
- Until the drive is unplugged and plugged back in, the system may serve the files from memory. Use the replug step for a read figure from the drive itself.
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