Is my USB flash drive fake? How to check its real size
Check whether a USB flash drive is falsely reporting its capacity, verify how much data it can really store, and tell fake size from slow speed.
Your USB flash drive says it holds 128 GB, but you are not sure it can really store that much. A counterfeit drive can report a large capacity while saving data only to a much smaller amount of memory. Files may look fine at first, then become damaged or disappear when you add more.
The Fake USB & SD Check writes test data to a drive and reads it back to check how much storage works. Use the separate USB & SD Speed Test if you also want to measure how quickly the drive reads and writes data.
Check the drive's real capacity
- Open the Fake USB & SD Check in Chrome or Edge on a computer. The tool needs browser access to the removable drive. Other browsers may offer a reduced version or no access.
- Back up anything you need from the drive, then use an empty drive if possible. The check writes data to the drive and can use its available space, so do not run it on a drive with important files unless they are safely copied elsewhere.
- Connect the USB drive directly to the computer, rather than through a hub if you can. Follow the tool's prompts to choose the removable drive and allow access.
- Start the capacity check and leave the drive connected while it writes and reads the test data. A larger or slower drive can take a while. Do not unplug it or close the browser during the test.
- Read the result and compare the amount of storage verified with the capacity printed on the drive or its packaging. If you also want to check performance, open the USB & SD Speed Test and test the same drive.
Do not use the drive for files you cannot replace until the check finishes successfully. Afterward, inspect the drive and remove any test files that remain, if there are any.
What the result means
The check verifies about the advertised capacity
The drive stored and returned data across roughly the amount of space it claims to have. That is a good sign, though it does not guarantee the drive will never fail. Keep a second copy of important files, as you would with any storage device.
The check verifies much less than the advertised capacity
The drive may be counterfeit, faulty, or both. Some fake drives report a large size to the computer, but their real memory is smaller. When you write past that real limit, new data can overwrite earlier data or fail to read back correctly. Do not trust the advertised capacity for important files.
The check stops or reports read errors
A failed check can point to a fake drive, but it can also mean the USB connection is unstable or the drive is damaged. Try another port and repeat the check once. If the same problem appears, treat the drive as unreliable rather than saving files to it.
The capacity check passes, but the drive is slow
Slow performance alone does not mean the drive is fake. The USB port, the drive's age, and the type of memory can all affect speed. The USB & SD Speed Test measures actual read and write speed, but it does not replace a capacity check.
The computer shows the advertised size
That number is not proof that all the storage works. Windows File Explorer and macOS Finder can display the capacity reported by the drive's controller, even if the physical memory cannot store that much. The write-and-read check is what tests whether data can be kept across the space.
What to do if the check fails
- Try a different USB port. Connect the drive directly to another port on the computer. Avoid moving or disconnecting it while the check is running.
- Repeat the check on an empty drive. Copy your files somewhere safe first. A second test can help rule out an interrupted connection, but repeated failures are a reason not to trust the drive.
- Check the drive on another computer. Run the capacity check again in Chrome or Edge. If it still verifies far less space than advertised, the problem is likely the drive, not one computer's file display.
- Keep a copy of any files you can still read. Stop adding files. Copy readable data to a known-good drive, and check that the copied files open before you erase or discard anything.
- Return or replace the drive. If it is new, contact the seller for a refund or replacement. If it is old and still fails after another port and computer, retire it. Formatting can change how a drive is organized, but it cannot create missing memory or repair failing hardware.
Why fake drives can look normal at first
A computer asks the drive how much storage it has, and the drive reports a number. In a counterfeit device, that report can be much larger than the actual memory. The operating system may let you copy files until the real storage fills up, so the drive can appear normal during a quick check of its properties.
The capacity test checks by writing data and reading it back, which is why it can reveal problems that a displayed size cannot. Test a new drive before using it for the only copy of photos, work, or backups.
