Boot Camp Assistant won't let me adjust Windows 10 partition size

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Level 1

7 points

Boot Camp Assistant won't let me adjust Windows 10 partition size

Hello.

Recently I installed Windows 10 through Boot Camp Assistant. I am currently considering removing and reinstalling it, because the partition size for it is unnecessary big and I want it to be smaller.

However, during installation a problem occurred which I wasn't able to solve then and need help with.

While setting up the installation, Boot Camp gave me the option to choose the size for the Windows partition. I read that for installing Windows 10, it needs at least 20 GB of free space. I only need to install one program on the Windows 10 partition of roughly 4 GB and was thinking of leaving another 4 GB or so free in case I need it. Keeping that in mind, I wanted to set my partition to 28 GB or so. However, this was not possible as the smallest possibility I could choose was 40 GB or so.

In this moment I went with it, but right now (without having anything installed on the Windows partition yet) I have another 18 GB of free space left (see below).

I don't need all that space on that partition and since I only have a 120 GB disk, I'd love to get that 10 GB or so back to my Macintosh HD partition.

Why couldn't I go below the 40 GB during the installation and how can I do this when I reinstall it?

MacBook Air 13″, macOS 10.15

Posted on Nov 16, 2020 3:39 PM

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Answer 1

Loner T

Level 9

59,536 points

Nov 17, 2020 10:56 AM in response to diverqent

diverqent wrote:

Is it possible to make the Windows partition smaller while installing it? As BCA seems to make overestimations and I have lots of space left that I don't need on the Windows partition.

No.

However, since you have a 2012 Mac, you can remove Windows in it's current state, create a smaller FAT32 partition and the Hybrid MBR manually, and then try to install Windows using the USB2 Flash drive that you have, and does not need to be recreated.

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Answer 2

Loner T

Level 9

59,536 points

Nov 16, 2020 3:56 PM in response to diverqent

diverqent wrote:

Why couldn't I go below the 40 GB during the installation and how can I do this when I reinstall it?

Windows creates hidden files which the BCA can only estimate. This is why a minimum size is chosen. You also need a 10GB partition for the Windows installer on 2015 and later Macs. This (OSXRESERVED) is later removed and given back to macOS.

Your 81GB macOS partition is fine. Assuming you are on macOS Catalina or older, if you decide to upgrade to Big Sur, you will need it.

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Answer 3

diverqent Author

Level 1

7 points

Nov 17, 2020 8:46 AM in response to Loner T

I don't mind reinstalling it. Although I am still not sure what the answer to my question is.

Is it possible to make the Windows partition smaller while installing it? As BCA seems to make overestimations and I have lots of space left that I don't need on the Windows partition.

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Answer 4

diverqent Author

Level 1

7 points

Nov 17, 2020 2:07 AM in response to Loner T

Since I'm on a 2012 Macbook I had to use a USB drive for the Windows installer, so I guess that wasn't calculated into it in my case, right?

I'm not entirely sure what you mean with "Your MacOS partition is fine". It works as supposed to, yes. But since I don't have much storage and also do video-editing with FCPX (which takes up huge amounts of space with its libraries sometimes) I can use all the storage I have.

For that reason I would like to trim down the Windows partition by 10GB or so.

Either way, does this mean there is no way to get it to be smaller if BCA makes these estimations (wrongly)?

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Answer 5

Loner T

Level 9

59,536 points

Nov 17, 2020 6:50 AM in response to diverqent

diverqent wrote:

Since I'm on a 2012 Macbook I had to use a USB drive for the Windows installer, so I guess that wasn't calculated into it in my case, right?

Correct. You should have used a USB2 Flash drive of 16+GB.

I'm not entirely sure what you mean with "Your MacOS partition is fine". It works as supposed to, yes. But since I don't have much storage and also do video-editing with FCPX (which takes up huge amounts of space with its libraries sometimes) I can use all the storage I have. For that reason I would like to trim down the Windows partition by 10GB or so. Either way, does this mean there is no way to get it to be smaller if BCA makes these estimations (wrongly)?

Since Windows is already installed, and if you choose not to re-install it, but reduce the size, look at commercial cloning software like Winclone. Also, for FCPX, you can add external storage to store larger files, if you need to.

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Boot Camp Assistant won't let me adjust Windows 10 partition size

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