Is My SD Card Fake? How to Check the Real Capacity of an SD Card on Android
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Cheap "1 TB" or "512 GB" cards are often fake: they report a big capacity but only store a fraction. Files written beyond the real size are lost. APPtoSD’s Is this card genuine? check finds out.
How the check works
The Full capacity check fills the free space of the card with test data, then reads every block back and checks it. It writes only into APPtoSD’s own folder on the card and needs no permission.
Run the check
- Insert the SD card and open APPtoSD.
- Tap Is this card genuine? ("Full capacity check – finds fake and failing cards").
- Read Before you start and start the check.
- Keep the phone charging. You can leave the screen: the check keeps running and shows its progress in a notification.
A full check of a large card can take hours. Android lets this kind of background task run for at most 6 hours a day; if the time runs out, the rest of the card was not checked and you can continue later.
What the result means
| Result | What to do |
|---|---|
| Genuine: every block came back exactly as written | The card is fine. |
| Fake: data past a certain point is lost | Copy your files off the card and don’t trust it with anything important. Ask the seller for a refund. |
| Errors found | Back up the card and stop using it for important files. |
| Write failed although space was left | The card is failing. Replace it. |
The test files are deleted when the check ends. If the card was removed during the check, they are deleted the next time the screen opens with the card inserted.
No app can repair a card. Formatting is done in Android’s own settings: see Do I Need to Format My SD Card? For speed, use the SD card speed test.