How to Resize a Mac Volume With Disk Utility

This article explains how to resize a volume with Disk Utility in macOS Catalina (2015) through OS X El Capitan (10.11).

How to Enlarge a Volume Using Disk Utility

You can enlarge a volume as long as it's not the last volume on the drive. You must be willing to delete the volume that is directly in back of the one you want to enlarge, along with its data.

Make sure you have a current backup of all data on the drive you plan to modify. Here's how to enlarge a volume.

1. Launch Disk Utility, located at Applications > Utilities.

   Or, type "Disk Utility" into Spotlight Search to bring up the application quickly.

2. Disk Utility displays a two-pane interface. Select the drive that contains the volume you want to enlarge.

3. Select Partition from Disk Utility's toolbar.

   If the Partition button isn't highlighted, you may not have selected the base drive, but one of its volumes.

4. Select Partition again to confirm.

5. You'll see a pie chart of all the volumes contained on the selected drive. You'll see what free space is available and how much space each volume occupies.

6. To make one volume bigger, you'll need to delete another. Select the volume you want to delete by clicking once within its pie slice. The selected pie slice turns blue, and the name of the volume is displayed in the Partition field. (In this example, we're selecting and deleting the volume More Stuff.)

7. Tap the minus icon at the bottom of the pie chart to delete the selected volume. The partitioning pie chart shows you the expected outcome of your action. Select Apply to continue or Cancel to stop these changes from being made.

8. If you applied the changes, the freed-up space is added to your remaining volume.

   You can also use the pie chart divider to adjust the size of the pie slices, but be careful; if a slice you want to adjust is small, you may not be able to grab the divider. Instead, select the small pie slice and use the Size field.

Resizing Without Losing Data in Any Volume

It would be nice if you could resize volumes without having to delete a volume and lose any information you have stored there. With the new Disk Utility, that isn't directly possible, but under the right circumstances, you can resize without losing data, although in a somewhat complicated manner.

For example, you have two volumes on your selected drive, Stuff and More Stuff. Stuff and More Stuff each take up 50% of the drive space, but the data on More Stuff is only using a small part of its volume's space.

You can enlarge Stuff by reducing the size of More Stuff and then adding the now free space to Stuff. Here is how to do that:

1. Launch Disk Utility and select the drive that contains both the Stuff and More Stuff volumes.

2. Select Partition from Disk Utility's toolbar.

3. Select the More Stuff volume from the pie chart.

4. Disk Utility allows you to reduce the size of a volume as long as the current data stored on it still fits within the new size. In this example, we'll reduce More Stuff to 45 GB. Next to Size, enter 45 GB and then press Enter or Return.

5. The pie chart shows the anticipated results of this change. Select Apply to commit to the new partitioning.

6. Select Partition to confirm. In the next section, we'll add the freed up space to Stuff.

Moving Data Using Disk Utility

Now we'll add the newly freed-up space to "Stuff."

1. Select the untitled volume you just created, and then select Restore.

2. Next to Restore From, select More Stuff, and then select Restore.

3. The restore process may take a few minutes. When it's finished, select Done.

Finishing the Resizing

Now, we'll complete the volume resizing process.

1. Select the drive that contains the volumes you've been working with, and then select Partition.

2. In the partition pie chart, select the More Stuff volume you used as the source in the previous section, and then select the minus button to remove it, adding its space to the Stuff volume.

3. The More Stuff data is restored to the remaining volume. Select Apply to finish the process.

4. Click Apply to finish the process.

The Rules of Resizing

Understanding how resizing works in Disk Utility will go a long way toward helping you resize a volume without experiencing any loss of information.

• When enlarging a volume, the volume or partition that is directly after the target volume must be deleted to make room for the enlarged target volume.
• The last volume on a drive can't be enlarged.
• The pie chart interface for adjusting volume size is picky. When possible, use the optional Size field to control the size of a drive segment instead of the pie chart's dividers.
• Only drives formatted using the GUID Partition Map can be resized without losing data.
• Always back up your drive's data before resizing a volume.

Resizing Wrap-Up

As you can see, resizing with the new version of Disk Utility can be simple, as shown in the first example, or convoluted as in the second example. In the second example, you could also use a third-party cloning app, such as Carbon Copy Cloner, to copy the data between the volumes.

So, while resizing volumes is still possible, it has become a multi-step process. Nevertheless, Disk Utility can still resize volumes for you; just plan ahead and be sure to have current backups.