SD card file transfer limit: why 4GB files fail and how to fix it

Why large files fail to copy

If an SD card refuses a file larger than 4GB even with plenty of free space, the card itself is almost certainly not broken. According to Engadget, the cause is usually the file system the card uses, most often FAT32.

FAT32 dates back to Windows 95 and remains popular because almost any device can read it. Its weakness is a hard cap on file size: no single file can exceed 4GB. The limit comes from the way FAT32 records file sizes with a 32-bit number, which tops out at 4,294,967,295 bytes, or nearly 4GB.

The card can physically store bigger files, but the file system blocks them. For documents and photos this rarely matters, but it becomes a real problem for large items such as 4K video.

The fix: reformat to exFAT

The solution is to reformat the card to exFAT, a newer file system designed to remove FAT32's restrictions, including the 4GB file cap. Engadget notes that exFAT is supported by Windows Vista SP1 and later, and by OS X Snow Leopard and later.

Before reformatting, back up everything on the card, because the process erases all data. Owners of very old equipment should also check compatibility first: a camera more than a decade old may not read exFAT, in which case staying on FAT32 is safer.

How to format on Windows and macOS

On Windows, open File Explorer and go to This PC. Right-click the SD card, choose Format, and pick exFAT as the file system. From the same window you can also rename the volume or run a Quick Format.

On a Mac, open Disk Utility, which you can find quickly with Spotlight. In the View menu, enable Show All Devices, then select the card itself rather than the volume beneath it. Choose Erase, set exFAT as the format, give the volume a name and confirm.

Once the card is formatted as exFAT, files larger than 4GB can be copied to it without trouble.

Switching back and what to watch for

If you later want FAT32 again, repeat the same steps and choose that file system instead. There is one catch on Windows: the operating system will not offer FAT32 for cards larger than 32GB. Engadget says you would need Terminal or third-party software to do that.

For most people, exFAT is the better choice on modern devices. It keeps broad compatibility while lifting the file size ceiling that FAT32 imposes.