How to “resize” your macOS Bootcamp [Tutorial]

Posted on by drvspan

I’m sure, that since you landed on this page, you are already frustrated with the web results and tutorials about “How to increase Bootcamp partition” or, “How to add extra space to your Bootcamp windows installation” that you have on your iMac or MacBook (Pro or not) or mac mini.

Well… the short answer is YOU CAN’T.

At least you cannot do it safely, as MacOS is the master of your hard drive, and thus, your hard drive schema implementation. The answer here, as Apple suggested while you installed your windows in your Mac, It’s not possible to change the size of the partition after installing Windows, but you can remove the partition and create a new partition of the correct size. Don’t try to resize your partition with Windows or a third-party app…. a bummer.

But if you are like me, this will not stop you, it’s just a new fun project for you. You have to find a way, without external drives, to increase your windows usable size without being left with just a few GB usable for your MacOS operating system.

The trick here is that you will not increase the actual BootCamp partition, but you will give extra space to your Windows installation by creating a new disk from your existing macOS storage. And the Upside of this is implementation is that this shared disk (I named mine as “buffer”) is going to be usable from Both Windows and MacOS.

But let’s cover the basics:

First of all, you have to choose the sizes of your partitions that you are going to use. My implementation on a 500GB Macbook pro is:

  • MacOS Partision size: 240GB
  • Windows Partition size: 130GB (This was my first bootcamp size selection when i installed Windows)
  • Buffer partition size: 130GB

Before the Buffer partition, my schema was 370GB for MacOS and 130GB for windows.

In order to do the same, you will have to use some simple steps (That include some command line commands as well)

Initially, you will have to decide depending on your needs, how you want to partition your disk. i’m waiting, it’s not gonna take long.. maybe…

After that Get things ready. And by get things ready I mean
TAKE A BACK UP of your mac os partition using your favorite software.
Mine was a backup using the build-in time machine for macOS. I haven’t backed up my windows implementation, since is used mostly for gaming and some Windows application that I am coding. But all the codes and libraries are already backed up in my private cloud. So I didn’t really care about my partition, but I didn’t want to delete it, as it was already implemented well and I had everything I needed configured.

Now that you are ready, follow these steps:

  1. Do not try yet to decrease the size of yoru macOS partition, as you won;t be able to do it. You partition might seem empty but “hidden” local timemachine snapshots are filling up your disk. Therefore Disk Utility is unable to decrease the size of your macOS, but if you tryed to do it, you will see the following message on the bottom right side of your disk utility.
  2. Delete your local timeMachine snapshots.
    • Go to System Preferences > Time Machine.
    • Uncheck the box “Back up Automatically”
    • This may take a while to delete the local snapshots, and there is no way to tell from the GUI if the snapshots are deleted. therefore, you have to wait, or use the terminel to delete them manually.
    • If you want to delete them manually, open up your favorite terminal app (mine is iTerm)
    • Run the following command to check about snapshots:
      tmutil listlocalsnapshots /
    • If you see am empty list, you are fine :
    • But if not , then you have to delete the snapshot your self.
    • you can do this one by one using
      sudo tmutil deletelocalsnapshots <snapshotname>
    • Or using CLI programming and delete them on a loop
      for d in $(tmutil listlocalsnapshotdates | grep "-"); do sudo tmutil deletelocalsnapshots $d; done
  3. After you delete your local snapshots via the command or manually, you will be able to resize your disk. BUT i advize you DON’T! it will take time and you are already mounted to this partition.
    SO shutdown your computer and start it in Recovery mode by pushing the button to start your computer and imediatly press and hold down the Command + R keys untiul you see an apple logo or spinning globe appear.
  4. When you boot into recovery choose Disk Utility
  5. While you are in disk Utility unmount the container disk that holds your Mac-HD and hit The partition button
  6. Then select the Mac-HD parition and Decrease the size to your selected size. This spet might take significant time to complete. BE PATIENT and do not interupt the process.
  7. Last and final step is to select the newlly appeared “Unallocated space” and format is Using ExFAT format. ExFAT format is a format recognized from both windows and MacOS.
  8. After you complete step 7, hit apply, finalize the settings, and reboot your computer.
    • If you reboot to MacOS, you will see the extra container partition to your locations in finder.
    • If you Boot to your windows you will see inside MyComputer a new partition Marked as D: buffer
  9. Remember, when you boot back into your macOS, re-enable the automatic buckups from TimeMachine settings!

Congratulations, you have created a new partition, usable both from your MacOS and your Windows, and you can save and transfer files between your two operating systems, from both your operating systems.
Now it’s time to install your extra programs, move some files around and free this overly full C: drive.

It wasn’t that hard now was it? If i can write this article from memory, two weeks after I’ve done the procedure, i’m sure that you will be able to perform the operation.

WARNING, it took me about 2.5 hours to complete the operation, but I was in trial and error mode, trying to figure out what and how to increase the size of my windows. After I thought of a not increase, but divide and conquer method, I just had to open my beer, wait for the command to execute, and install the new game that I wanted to play from my internal SSD, and not from an external disk that I would have to carry around.

for any questions, you are welcome to write me some comments.

If the procedure is not clear or is missing a step… I did my best to write it down (two weeks after I’ve done it) but I would be happy to edit the article and correct the procedure.

Happy coding and editing everyone!