How to check a fake microSD card after formatting

You changed the file system on a microSD card and want to know if it still has its advertised capacity. A format can make the card look empty and ready to use, but it cannot prove that the card is genuine or that every part of its storage works.

Test the card after formatting it to the file system you plan to use. The Fake USB & SD Check writes data across the card and reads it back to check whether its reported capacity holds up. The test fills the card, so copy off anything you need first.

Test the card after changing its file system

1. Back up any photos, videos, or other files on the card to a different device. Use a blank card for testing, because the test writes data across its available space.
2. Format the card to the file system you intend to keep using. If you have not formatted it yet, do that before testing. The test needs a mounted card with available storage.
3. On a computer, open the Fake USB & SD Check in Chrome or Edge. The tool works best in those browsers on a computer. Insert the card through a reader and follow the prompts to select it.
4. Start the capacity check and leave the card connected until the write and read-back process finishes. Do not remove it, close the browser, or let the computer go to sleep during the test.
5. Review the result. If the test did not finish, check the fixes below before deciding the card is faulty.

Run the check after your final format, not before. Formatting changes how the card organizes files, but does not increase its physical storage. A successful test checks that data written across the card can be read back, which is more useful than relying on the capacity shown by your computer alone.

What the result means

The full check completes and data reads back

The tested storage accepted and returned the test data without an error. That is a good sign that the card can use the capacity tested. It does not prove the card is from the brand on its label, guarantee its speed, or promise that it will never fail. Keep a separate copy of important files.

The check reports a smaller usable capacity or read-back errors

The card may have less real storage than it claims, or it may have a fault. Counterfeit cards can report a large size while overwriting earlier data once the real storage fills. If the error happens again after you format the card and test it in another reader, do not trust it with important files.

The check stops before finishing

A full-card test can take time, especially with a slow card or reader. A disconnected reader, a locked adapter, a computer going to sleep, or a browser permission problem can also interrupt it. Reconnect the card and check the setup before treating an interrupted test as a capacity failure.

Your computer shows less space than the label

A small difference is normal. Card labels use decimal units, while many systems display capacity using a different unit convention. Formatting also uses some space for file system information. A modest difference in displayed free space is not, by itself, evidence that the card is fake.

Fix problems that interrupt the test

1. Check that you selected the card. If more than one removable drive is connected, confirm the selected location by its name and capacity. Do not select your computer's internal drive.
2. Use a supported browser on a computer. Run the check in Chrome or Edge on a computer, then allow the browser to access the card when prompted. If you are on a phone or using another browser, switch to a computer for this check.
3. Check the card and adapter. Some full-size SD adapters have a small lock switch. Set it to the unlocked position, then reconnect the card. Also try another USB port or card reader.
4. Format the card again if needed. On Windows 11, open File Explorer › This PC, right-click the microSD card, choose Format, select the file system you want, and start. On macOS, open Disk Utility, select the card's volume, choose Erase, select a file system, and confirm. Check the selected device carefully so you do not erase another drive.
5. Format it on the phone if that is where it will be used. On Android, open Settings › Storage, select the SD card, and choose the format option if available. Menu names vary by phone. Back up the card first, since formatting erases its contents.
6. Try a different reader and repeat the test. If the card passes in one reader but fails in another, the reader, adapter, or connection may be the problem. If it fails repeatedly in separate readers, stop using it for valuable data.

When the card may be faulty

A repeated read-back failure is a reason to replace the card, especially if files disappear, change, or become unreadable after copying. Test it in another reader before making that decision, and keep any purchase receipt or test result if you plan to request a refund. Do not keep using a card that fails a capacity check for important photos or recordings.

Choose a file system that suits your devices

File systems affect which devices can use a card and how large an individual file can be. FAT32 is widely supported, but it cannot store a single file larger than 4 GB. exFAT is commonly used for larger files and removable storage, though an older device may not support it. Check the requirements for the camera, phone, or other device before formatting. Then run the capacity check on the newly formatted card.

After testing, format the card again if you want a clean card for normal use. Keep the backup until you have confirmed that the card works in the device where you plan to use it.