Big Sur Install - GB Space Needed

Excerpted from How to upgrade to macOS Big Sur - Apple Support:

"If upgrading from macOS Sierra or later, macOS Big Sur requires 35.5GB of available storage to upgrade."

NONE of those is the Culprit, as I indicated, you would get "no disks available for Install" rather than "not enough space".

Apple File System (APFS) freely re-apportions and shares all the space on the drive as needed -- the old "Hard" boundaries between logical drives are a thing of the past.

You simply need to allow for the larger number -- 45GB free.

That number only applies if upgrading from Sierra or later.

If upgrading from macOS Sierra or later, macOS Big Sur requires 35.5GB of available storage to upgrade. If upgrading from an earlier release, macOS Big Sur requires up to 44.5GB of available storage. 

TIP: move storage like non apple apps or non apple application support from your computer to a USB-stick or external drive. Use ICloud storage for photos, mail etc.

Yes. Backup, reformat the drive, and start over.

👍

I delete my GarageBand Library to free up an additional 17 GB which completed the 35 GB needed to install Big Sur. This worked.

That's a great suggestion!

CAUTION: if installing from a Bootable USB stick, you are effectively Not installing while running High Sierra, and may therefore require 44.5GB free space on the boot drive, not the lower number.

Installer usually has no problem fiddling around with Boot Drive partitions and formatting. Unsolvable problems in that area would give you "No drives available for Install", rather than "Not enough space".

Even when you install from a Bootable USB-stick, the first part of the Install process is to copy all the files to the destination drive.

It is possible Apple did not calculate the recommendations properly, assuming your had an ADDITIONAL 35GB available AFTER the download was copied onto the drive. Or perhaps since you are booting form a USB-stick, you need to follow the LARGE-sized recommendation, the 44.5 GB size.

Apple states " If upgrading from macOS Sierra or later, macOS Big Sur requires 35.5GB of available storage to upgrade." Okay, but why am I getting this response when I am trying to completer my upgrade. Once I get past the point where I click the Install macOS Big Sur button and then read and agree click and then click continue and am given the choice of which drive to install to, I go to choose Macintosh HD and I get the message that I need 13.99 GBs more space. Trouble is under the storage tab when I look via About this Mac it states that there is 40.72 GBs available. ??? I am install from a bootable USB installer as you can see I don't have enough space to install from the internal drive. I have already dumped most of my third party software off of the Macintosh HD. When I formatted the USB prior to the Installer formatting it I used MacOS Extended (Journaled) scheme APM (Apple Partition Management). Should I have instead used the GUID scheme in the formatting prior to the reformat to a bootable media? TIA.

Here is another screenshot of my disk system. I noticed when I looked back that the 40.72 seems to be spread out over two partitions. Correct? Plus I also noticed that the partition map in the Media disk is a GUID Partition Map and not the Apple Partition Map I had formatted the USB in prior to be re-formatted to be bootable installer. Either way, which one or any of these the culprit?

Exactly! Apple hasn't yet address this issue for those of us who purchased Macs [desktop or notebook] with the 128 GB drive. it hurts even more as this was my foray into a Mac. My daughter bought me a Mac mini 2018 for my sixtieth birthday. in retrospect I should have paid for the upgrade to the 256 GB drive. I too am on the fence about this. if I trade-in to new release of there mini just announced I get $420 trade value, less than half of what she paid for it [in mint shape]. Plus, ironically the base model now comes with a 256 GB drive [again soldered I'm assuming]. That partitioning of the Macintosh drive that small is to me an epic fail. they should have either made the 2018 base model with a 256 GB or not partitioned the 128 GB and advised buyers to buy an external drive which I would have regardless of the configuration. Unless Apple makes a lite installer for this of us who have 128 GB. I really like my Mac, but I can't keep dropping that type of dime every time a significant upgrade occurs with such frequency, especially as I am now also retired. Oh well, I will try to upgrade again today.

Running the above. I've decided to take a break from this process because a) this upgrade has been as painful as a Windows upgrade was, and b) Looking at the Big Sur discussions it confirms a). Easily the most horrible release in Apple's history!

I've been removing virtually every file I can think of and most applications, trying to get this to work. The finder window says I have 76.64 GB available; the About This Mac > Storage reads 86.82 GB available. Do I have to completely wipe my computer to be able to upgrade? I've been trying to do this for four days and fortunately there is Google for information, as Apple doesn't seem to mention this issue nor how to fix it.

I have a 2019 13" MacBook Pro with the i7 processor, but only 128 GB drive. Since this machine was intended mostly for work in my office and occasionally for travel, paying the high cost for a bigger drive didn't seem a good choice. I never would have thought that it would preclude upgrading the OS. Non-upgradable hardware I knew about; non-upgradable software they never mentioned.