How to test memory cards after a bulk purchase
Test each memory card's real capacity, catch counterfeit or faulty cards, and know how to document results before a return deadline.
A bulk order of memory cards can look fine at first, even if some cards are counterfeit or faulty. A card may show the advertised size on your computer but fail when you try to store more data than it can really hold.
Test every card before relying on it. The Fake USB & SD Check fills a card with test data and reads it back, so you can check the capacity rather than trusting the label.
Test every card before using it
- Back up anything you need from the card. Use an empty card for the test, since the check writes data and may use the available space.
- Put one card in a reader connected to a computer. Test cards one at a time so you can match each result to the right card.
- Open the Fake USB & SD Check in Chrome or Edge on a computer. The tool uses browser access to work with the card. If the browser asks you to choose a location, select the card, not another drive.
- Follow the on-screen instructions to start the check. Leave the card connected while the tool writes and reads the test data. A large card or a slow reader can take a while.
- Note the card's labeled capacity and whether the check completes or reports an error. Repeat the same process for each card in the order you received them.
Keep the cards in order while testing. If they have no useful serial numbers, put a removable label on each card or its case and record which one you tested. That makes it easier to return only the cards that fail.
What the result means
The check writes and reads the expected capacity
The card passed this capacity check in the reader you used. That is a good sign, but it does not prove the card will last forever or work in every camera, phone, or card reader. Keep a separate backup of important files.
The capacity shown by your computer may look smaller than the number on the packaging. Manufacturers label storage in decimal units, while operating systems may display a smaller binary value. For example, a card labeled 128 GB may appear near 119 GiB, with some additional space used by formatting. That difference alone does not mean the card is fake.
The check reports errors or cannot complete near the card's labeled size
The card may have less real storage than its label claims, or it may have faulty memory. Some counterfeit cards report a large capacity to the computer but overwrite earlier files when the smaller real storage fills up. A write-and-read check can uncover that problem.
The check fails well before the labeled capacity
That can point to a damaged card, an unreliable card reader, or a poor connection. Do not assume the card is counterfeit after one failure. Repeat the check with the same card in a different reader or USB port before deciding.
The card does not appear or cannot be selected
The computer or browser may not have access to it. Check that the card is seated properly, that the reader supports its type, and that you are using Chrome or Edge on a computer. The tool may offer reduced support or none in other browsers.
How to fix a failed or incomplete test
- Check the card's write-protect switch. Some SD cards, and SD adapters used with microSD cards, have a small lock tab on the side. Move it to the unlocked position, reinsert the card, and try again.
- Reconnect the card and reader. Remove and reseat the card, then connect the reader directly to another USB port instead of a hub. If possible, try a second reader that supports the card's format.
- Use a supported browser on a computer. Open the tool in Chrome or Edge, then respond to any browser prompt that asks for access to the card. On a phone or tablet, the browser may not provide the file access the test needs.
- Format the card only after backing up its contents. Formatting erases files and can sometimes clear a filesystem problem, but it cannot add real storage or repair failing memory. In Windows 11, use File Explorer › This PC › right-click the card › Format. On macOS, open Disk Utility, select the card, and choose Erase. Make sure you have selected the card, not your computer's internal drive.
- Repeat the full check with another reader. If the card still fails, or reports errors at a similar point, stop using it for important files. A quick format or a capacity number shown by the operating system is not a substitute for a complete write-and-read check.
When to return the card
If a card fails the full test in two readers, treat it as unreliable. Do not put it in a camera or phone for an important trip, and do not try to fix a card that repeatedly loses or corrupts data. Save the order details, a photo of the card's label, and the test result for the seller. Contact the seller before the return window closes, and keep the failed card until the return or refund is resolved.
After testing, check the card's contents and remove any test data before using it normally. The test runs in your browser, and the card data stays on your device.
