Tool
Spotting fake card capacity
A card that claims more than it has loses data without any error message.
The short answer
Counterfeit cards are a common and invisible cause of data loss.
Manipulated cards report a higher capacity to the system than physically exists. As long as you stay below the real limit everything works. Data written beyond it vanishes or overwrites earlier recordings — usually without any warning.
01 / Calculate
A first assessment from the numbers
Enter the advertised capacity and the usable figure your operating system shows. A deviation of about seven percent is normal and comes from the different ways gigabytes and gibibytes are counted.
02 / Test safely
The real test writes to the card
Arithmetic is only an indication. Certainty comes only from a test that fills the card completely and reads it back. Established tools for this are H2testw on Windows and F3 on macOS and Linux.
- 1
Recover and back up everything you still need from the card first.
- 2
Only then format the card and start the capacity test.
- 3
Let the tool write and read back the entire free space.
- 4
If the verified capacity differs markedly from the advertised one, stop using the card for important recordings.
A capacity test overwrites the entire card. Run it on an empty card only. If you still want to recover recordings, the order is mandatory: recover the data first, test afterwards.
Sources and technical references
Common questions
Why does my 64 GB card show only about 59 GB?
That is normal. Manufacturers count in decimal gigabytes while many operating systems display gibibytes. The resulting gap of roughly seven percent does not indicate a counterfeit.
Can I recover data from a fake card?
Whatever actually sits in the real storage and has not been overwritten can generally be readable. Anything written beyond the true capacity, however, never physically existed and cannot be recovered.
Does this tool check my card directly?
No. It only calculates with the values you enter. A browser cannot access a raw device, and a real test would have to write in any case.