How to check a fake SD card before a camera shoot

A card can show the advertised capacity on its label and still hold far less data. The problem may stay hidden until a camera fills the card, when older photos or video can be overwritten or lost.

Check the card before trusting it with a shoot. TooLab's Fake USB & SD Check fills a USB drive or SD card with test data, then reads it back to check how much storage really works. The test runs on a computer in Chrome or Edge, not on a phone.

Check the card safely

1. Open the Fake USB & SD Check in Chrome or Edge on a computer. Connect the SD card through a card reader, then choose the card you want to check.
2. Back up the card first. The test writes data across the card. Copy any photos or files you need to another location, and do not use the test on the only copy of anything.
3. Check the card's label or packaging so you know its advertised capacity. Make sure the computer has selected the SD card, not another external drive.
4. Run the capacity check and let the write and read-back process finish. Keep the card connected, and avoid using it in the camera during the test.
5. Compare the test's usable capacity with the card's advertised size. A small difference in the number shown by your computer can be normal because manufacturers and operating systems count storage differently.
6. After the capacity check passes, use the USB & SD Speed Test if you also want to check transfer speed through your card reader. Treat that result as a reader-and-computer test, not a guarantee of the camera's recording speed.

Testing may take a while, especially on a large card or a slow reader. Don't unplug it just because progress seems slow. If the browser cannot access the card, check that you are using Chrome or Edge on a computer and grant access when your browser asks.

What the result means

The test writes and reads the expected capacity

The card passed this capacity check under the conditions tested. That is a good sign, but it does not verify the seller, brand, card condition in every situation, or whether the card is fast enough for your camera. For important work, test the card before the shoot and keep a second copy of your footage.

The usable capacity is much smaller than the label

This is a strong warning sign. Some counterfeit cards report a large capacity to the computer but cannot reliably store data beyond their real limit. When the limit is reached, new data may overwrite earlier files or fail to read back correctly. Do not use the card for the shoot.

The test reports errors or stops before finishing

The card, reader, connection, or browser access may have failed during the test. An error does not prove by itself that the card is counterfeit, but it means you should not trust it with your photos yet. Check the connection and try again with a different reader before deciding whether to return the card.

The capacity is right, but the card is slow

A capacity check does not measure whether a card can keep up with high-resolution photos or video. A slow card can cause a camera to pause, stop recording, or take longer to clear its buffer. Check the speed class your camera requires and compare it with the card's markings. A browser speed test through a reader is only a clue because the reader, port, and computer can limit the result.

What to do if something looks wrong

1. Reseat the card and reader. Remove the card safely, insert it again, and check that it sits firmly in the reader. If you use a full-size SD adapter, check its lock switch. That switch can prevent writing, though it does not establish whether the card has real capacity.
2. Try another USB port or reader. A loose connection or unreliable reader can interrupt a write or read-back. Connect the reader directly to the computer rather than through a hub, if possible.
3. Check that you selected the right drive. On Windows 11, open Settings › System › Storage › Advanced storage settings › Disks & volumes to review connected drives. On macOS, open Applications › Utilities › Disk Utility and identify the SD card by its name and capacity. Do not erase or format a drive just to identify it.
4. Repeat the test after checking the connection. Use the same card with a known-good reader, or check a known-good card with the same reader. If the problem follows the card, the card is the likely cause. If it follows the reader, replace or troubleshoot the reader instead.
5. Format the card in the camera only after the test passes. Back up anything you need first. Use the camera's own format option before a shoot, since it prepares the card for that camera. Formatting cannot make counterfeit capacity real or repair faulty storage.
6. Stop using a card that repeatedly fails. Return it to the seller or contact the manufacturer if it is covered by a warranty. Do not use it for the only copy of client work, travel photos, or other important footage.

Capacity is not the same as camera compatibility

A card can have its full advertised capacity and still be a poor match for a camera. The camera may require a particular card type or minimum sustained write speed, which is the speed it can maintain while recording. A short speed test through a computer reader cannot prove that the card will sustain a long video recording in your camera.

Check the camera manual for supported card types and speed requirements. Before the shoot, format the tested card in the camera, record a short clip at the settings you plan to use, and play it back. For an important shoot, bring another tested card and copy the files to a separate drive afterward.