Test a microSD card's real capacity after formatting
Formatting a microSD card does not prove its capacity is real. Test the full card with a write and read-back check, then decide whether it is safe to use.
You formatted a microSD card, and the computer shows the expected storage space. That still does not prove the card can store that much data. Some counterfeit cards report a larger capacity than they can actually use, so files may be lost or corrupted when the card fills up.
Run a full write and read-back check before trusting the card with photos, videos, or backups. The Fake USB & SD Check fills the storage and reads the test data back to help find the card's real usable capacity.
Test the card after formatting
- Back up anything you need. Move the card's files to another drive first. A capacity check writes test data to the card, so use an empty card and do not keep important files on it during the test.
- Use a supported browser and reader. Open the Fake USB & SD Check in Chrome or Edge on a computer. Insert the microSD card into a reliable card reader, then connect it to the computer.
- Choose the microSD card. Follow the tool's prompts to select the removable card, not your computer's internal drive or another external drive. Check the drive name and capacity before continuing.
- Run the full check. Let the tool write test data across the available storage and read it back. Keep the card connected, prevent the computer from sleeping, and do not remove the reader while the check is running.
- Review the result before using the card. Note the amount of data that passed the read-back check. If the test reports errors or a much smaller usable capacity than the label claims, do not trust the card with files you cannot replace.
Formatting prepares a file system so your devices can organize files. It does not necessarily write and verify data across the entire card. A quick format, in particular, usually changes file system information without checking every storage area. A full write and read-back check is a separate test.
What the result means
The full capacity passes the read-back check
The card stored and returned the test data during this run. That is a useful sign that its reported capacity is usable, but it is not a guarantee against every future failure. Eject the card safely, then put your files on it and keep another copy of anything important.
The test finds errors or stops at a lower capacity
The card may have less real storage than it reports, or it may have unreliable memory or a connection problem. Counterfeit cards often accept data at first and then overwrite earlier data when their true capacity is exceeded. A format cannot fix that. Do not use the card for important photos, recordings, or backups.
The usable amount is a little below the label
A small difference can be normal. Manufacturers usually label capacity in decimal units, while operating systems may display storage using binary units. The file system also uses a little space for its own information. For example, a card labeled 128 GB may show roughly 119 GiB before that overhead. A large shortfall is not explained by this unit difference.
The test cannot access the card or ends unexpectedly
The browser, card reader, adapter, or operating system may be blocking access or losing the connection. This result does not by itself prove that the card is counterfeit. Check the reader and browser, then retry once with the card empty and securely connected.
How to fix a failed or interrupted test
- Reconnect the card and reader. Safely eject the card, remove it, and insert it again. If you use a microSD-to-SD adapter, make sure it is seated firmly. The adapter's lock switch can prevent writing, so check that it is not set to locked.
- Allow access in a supported browser. Use Chrome or Edge on a computer, and follow any browser prompt to grant access to the removable storage. If you are using another browser or a phone, switch to a computer with Chrome or Edge for this check.
- Try another port or reader. Connect the reader directly to another USB port instead of through a hub. If possible, test the reader with a known-good card, or test the microSD card in a different reader. This helps separate a card fault from a reader or adapter problem.
- Format only after backing up, then retest. Formatting can clear file system problems, but it cannot add real capacity to a counterfeit card. On Windows 11, open File Explorer › This PC, right-click the card, and choose Format. On macOS, open Disk Utility, choose View › Show All Devices, select the card's volume, and choose Erase. Check the selected device carefully so you do not format the wrong drive.
- Stop using a card that fails again. If the same errors return after reconnecting and checking the reader, treat the card as unreliable. If it is new, contact the seller for a refund or replacement rather than relying on it for storage.
When the card is the problem
A card that reports more capacity than it can verify is not made reliable by reformatting, changing its file system, or trying another phone. If the result is consistent across a second reader or computer, stop writing data to it. Return it to the seller if you can, and replace it with a card from a source you trust.
Even a card that passes a capacity check can fail later. Keep a second copy of important files, and safely eject the card before removing it from a computer or reader. The Fake USB & SD Check runs on your computer, and the card's contents are not uploaded to a server.
