How do I format an SD card that only reads on my Mac?

Some SD cards have physical write-protect switches. If yours does not, then determine if it appears in Disk Utility: Disk Utility User Guide for Mac - Apple Support

Intro to Disk Utility on Mac - Apple Support

If your SD card is only readable on your Mac and you can't write or format it, there are a few possible reasons:

• The card is write-protected (check the physical switch on the SD card).
• It's formatted in a read-only file system (e.g., NTFS, which macOS can only read).
• It has corruption issues preventing modifications. (Bad sectors or file system issues)

First, check if the write-protection switch on the side of the SD card is unlocked. If it is locked, slide it to the unlocked position. If the issue persists, try formatting the SD card on a Windows computer. Or try to select a different partition map when formatting.

If the card is to be used in a digital camera, it should be formatted in the camera. (There are also special formatting tools on the SD Association site that they recommend using if you must format a SD-family card in a computer)

First, check your SD card and ensure the write protection switch is not set to 'locked.' This physical lock will prevent writing to or formatting the card. You can also test the SD card in a camera or another Mac/Windows computer to see if it works there.

Next, check the file system format of your SD card. If it is formatted as NTFS, note that macOS can read NTFS drives but cannot write to them natively. To enable writing, you can use a third-party driver like iBoysoft NTFS for Mac to automatically mount your SD card and allow writing without the need to reformat it to exFAT, HFS, or APFS.

If you still want to reformat the SD card, try using Disk Utility again and ensure you format the card at the device level (not the volume level). If reformatting fails, connect the SD card to a Windows computer, copy all files to a safe location, and then run the 'clean all' command in DiskPart to erase your SD card. Afterward, you can reformat it to exFAT, which is fully supported on macOS.