Fake Flash Drive Checker
Find out if a USB stick, SD or microSD card really holds what the label says. The checker fills the drive with unique test data, reads every byte back and shows exactly how much is real, in the same way as H2testw and F3.
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Pick the USB drive or SD card itself, or an empty folder on it. Copy off anything important first.
Writes 1 GiB test files, then reads every byte back and compares it.
Everything happens on your computer: the test files are written to and read from the drive you choose, and nothing is uploaded.
How to use the Fake Flash Drive Checker
- Back up and empty the drive: the test needs free space, and fake drives can lose existing files.
- Press Choose drive folder and select the USB drive or memory card (or an empty folder on it), then allow editing.
- Keep Fill all free space ticked to test the full capacity, or enter a smaller amount in GB for a quick check.
- Press Start write + verify and wait: filling a 64 GB drive at 20 MB/s takes about an hour, plus the time to read it back.
- Unplug and reconnect the drive, choose it again and press Verify existing test files for a result that cannot come from your computer's cache.
- Read the report, copy it if you want to claim a refund, then press Delete test files.
What the results mean
| Result | What happened | What it means |
|---|---|---|
| Verified OK | The block came back exactly as written, byte for byte | This part of the drive stores data correctly |
| Overwritten by other test data | The block holds a valid test block from a different position | Classic fake capacity: the controller wrapped around and reused real memory |
| Empty or erased | The block is all zeros or all ones | Writes were thrown away, typical once a fake drive's real memory is full |
| Corrupted | The block has the wrong bytes | Failing or very low quality memory, a bad card reader or a loose connection |
| Missing | The test file is shorter than what was written, or gone | File system damage, often caused by a fake drive overwriting its own file table |
The usable capacity estimate is the amount of data checked before the first error. A genuine drive shows no errors at all; even a few bad megabytes mean the drive cannot be trusted.
Why a "64 GB" drive shows less than 64 GB
A drive sold as 64 GB has 64,000,000,000 bytes, which operating systems often show as 59.6 GB (actually GiB, 1 GiB = 1,073,741,824 bytes), and the file system uses a little more. So a real drive's usable space is usually about 90 to 93% of the label. A fake drive fails long before that: a "128 GB" drive that errors after 7.5 GB contains an 8 GB chip.
| Label | Bytes | Shown by Windows (GiB) | Typical free space after formatting |
|---|---|---|---|
| 16 GB | 16,000,000,000 | 14.9 | about 14.5 to 14.9 GB |
| 32 GB | 32,000,000,000 | 29.8 | about 29 to 29.8 GB |
| 64 GB | 64,000,000,000 | 59.6 | about 58 to 59.6 GB |
| 128 GB | 128,000,000,000 | 119.2 | about 117 to 119 GB |
| 256 GB | 256,000,000,000 | 238.4 | about 236 to 238 GB |
Tips for a reliable test
- Format the drive first (exFAT for drives over 32 GB) so all space is free and the file system is clean.
- Use a USB port directly on the computer, not a hub, and a known good card reader for SD cards.
- Keep the computer awake: turn off sleep while the test runs, and keep this tab open.
- Very cheap "2 TB" or "1 TB" sticks are almost always fake; checking the full capacity is the only way to be sure.
- For speed alone, use the USB drive speed test, which is much quicker than a full capacity check.
Frequently asked questions
How do fake flash drives work?
A fake drive has a small memory chip, for example 8 GB, with a controller programmed to report a much larger size such as 128 GB or 2 TB. Files seem to copy normally, but once the real memory is full, new data overwrites old data or goes nowhere. You only find out when files later turn out to be corrupted.
How does this checker detect a fake drive?
It writes 1 GiB test files where every 1 MiB block contains a signature with its own position and a unique pseudo-random pattern. It then reads everything back and compares it. On a fake drive, blocks come back corrupted, empty, or containing data from a different position because the controller wraps writes around the real memory.
Why should I reconnect the drive and verify again?
Right after writing, your operating system may still hold recently written data in RAM and return it from there instead of reading the drive. Unplugging the drive clears that cache, so Verify existing test files then reads only from the drive itself. On large fake drives the early files are usually long gone from the cache, so the first check already catches them.
Will this delete my files?
It does not touch your files; it only creates, reads and deletes files named ftctest-....dat. However, a fake drive can corrupt existing files once the test writes past its real capacity, so copy anything important off the drive first.
Which browsers can run the test?
It needs the File System Access API with folder access, which Chrome, Edge, Opera and Brave support on Windows, macOS, Linux and ChromeOS. Firefox, Safari and mobile browsers cannot write to a chosen folder, so use a desktop Chromium-based browser.
How long does the test take?
Time equals the free space divided by the write speed, plus the same space divided by the read speed. Cheap fake drives often write at 5 to 15 MB/s, so a claimed 128 GB drive can take several hours; a quick test of a few GB tells you less but finishes in minutes.
What should I do if the drive is fake?
Ask the seller for a refund with the copied report as evidence. If you keep using it, reformat it with a tool that can resize it to the real capacity shown by the report, and never trust it with important data.
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.