You can often format an SD card with whatever device you’re using it in. However, it can be quicker to use a computer, and you might want to use it only with a computer anyway. Here’s how to handle your card-formatting needs on macOS.
Connecting an SD Card to Your Mac
Plugging In an SD Card
First, there are two main methods of reading an SD card with a Mac. The easiest is to insert the card into a built-in SD card slot, but this is not available on every model. Most desktop Macs (aside from the Mac Pro) have an SD card slot, as do most MacBook Pro models before 2016, and some models of MacBook Air. However, since 2016, this integrated port has fallen out of favor with Apple, and the company tends to omit it to save space.
The standard alternative to an SD card slot is an SD card reader, which typically plugs into either a USB-A or USB-C port. Many USB-C hubs include an SD card slot, and general-purpose multi-card readers often handle SD cards alongside other card types.
Understanding Different SD Card Formats
There are many types of SD card, ranging in physical size and capacity format. The miniSD and microSD formats are physically smaller cards and are not supported natively by built-in Mac SD slots. But they can still be used with a passive adapter, a card that’s the same size as a full SD card, with a slot to house smaller formats.
Larger capacities are provided by the SDHC, SDXC, and SDUC formats for both SD and microSD sizes. Additionally, SDIO is supported by the standard SD and the less popular miniSD sizes. Although these details are largely unimportant, you should be aware of what actual capacity (e.g. 32 GB) your card is if you intend to totally reformat it.
Read more: The Fastest and Best microSD Cards
Using Disk Utility to Format an SD Card
Disk Utility is an app shipped with macOS. It should be present in your /Applications/Utilities folder. It can be used for many different disk-related purposes, on both internal and external storage devices.
Begin by selecting your SD card from the list on the left-hand side. If you’re using a Mac with a built-in SD card slot, it should show up in the Internal section. An SD card plugged into an external reader will show in the External section. Make sure you select the card itself, by name, rather than the physical device. It’s easier to do this if you select Show Only Volumes from the View menu in the top left.
Once you have the card selected, confirm that it’s the one that you want to format. You can check the capacity and used space, for example. Then click the Erase button at the top of the window. You can specify a Name for the card, and its Format.
Selecting a File System Format
If you’re formatting the SD card to use it in another device, such as a digital camera, you should avoid any Mac OS formats and select either MS-DOS (FAT) or ExFAT. Use FAT if the card is 32 GB or less, as all SD and SDHC cards are. Use ExFAT if the card is greater than 32 GB, such as an SDXC or SDUC card.
Using SD Card Formatter on macOS
A separate app might seem unnecessary since Disk Utility is built-in. However, SD Card Formatter is a friendlier alternative, dedicated to the task of formatting SD cards. It handles details such as the file system for you, and will even reformat an ExFat card as FAT12 if the latter is more efficient. It’s also free to download and use.
The app has a very simple interface with few options. First, select the card using the first dropdown menu. Typically, you’ll be working with one SD card at a time, and this will be selected for you. Check the capacity is what you’d expect. It won’t usually be the full amount advertised on the card, for several reasons, but it should be approximately equal.
There are two Formatting options available: Quick and Overwrite. Quick is the faster option because it frees up the space without actually erasing the raw data. The Overwrite method actually wipes the old data, so you should use it if security is a concern and you want to ensure the data cannot ever be recovered.
Finally, you can supply a Volume label which is a name for the SD card to help you recognize it later. It can be useful to include the capacity or the manufacturer in this name, particularly if you work with several different cards.
Using the Command Line
Do not use this option unless you are very confident!
You should have a deep understanding of terms such as file system format, partition. You should also recognize exactly which disk you are dealing with when shown a volume identifier such as disk2. Be very careful not to accidentally format the wrong drive!
With those caveats, the diskutil tool is the command-line equivalent of Disk Utility. Start by listing the available drives on your system:
You should be able to identify which is your SD card via its name. In the list of drives, you will see an identifier, typically something like disk2. You should make sure you are certain you are working with the correct device before continuing. To erase all contents, but keep the same underlying structure (file system), use the reformat command, for example:
If you want to change the file system, use the following advanced command:
The HFS+ is the type of file system you wish to use. You can see which file systems your version of diskutil supports with the following command:
The full man page gives detailed instructions on how to use this complex but powerful tool.
Troubleshooting Problems With SD Card Formatting on Mac
Trying to Format a Read-Only Card
SD cards have a physical switch lock which you can use to prevent accidental data loss. If a card is in read-only mode, you won’t be able to format it. Under Disk Utility, you’ll get an error, but the message itself can be quite cryptic:
The SD Card Formatter app gives a friendlier “Cannot format write protected card” error:
To turn read-only mode off, slide the switch towards the end with the contacts.
Formatting With an Incompatible File System
Using Disk Utility, it’s possible to select a file system that is incompatible with the SD card you are formatting. For example, trying to format an old 8MB card with the Mac OS Extended (Journaled) type can result in an error as shown:
With Plenty of Options, Choose the Right One for You
A tool like SD Card Formatter can simplify the process of formatting an SD card, but Apple’s built-in Disk Utility app can also do the job. Be careful to understand the differences between file systems, particularly when using an advanced tool such as diskutil on the command line.
