Two accounts on one Mac, and where the space actually goes
Each user has their own hidden folders and their own caches. How to see the whole disk, and what a shared folder does not solve.
On a shared Mac, the storage screen shows you your own account plus everything the system counts, and gives you no way to see what another account is using. That is a privacy feature and it makes a full disk genuinely hard to diagnose.
Seeing the whole disk
sudo du -sh /Users/* 2>/dev/null | sort -h
sudo du -xh -d 1 /System/Volumes/Data 2>/dev/null | sort -h | tail -15Run from an administrator account, that shows each user's total. It does not tell you what is inside another person's folder, which is correct, and the total is usually enough to know whose cleanup is needed.
What each account duplicates
| Duplicated per user | Typical size |
|---|---|
| Browser profiles and caches | 1 to 8 GB each |
| Photo libraries | Whatever their photos are |
| Mail and messages | Per account history |
| App caches and containers | 1 to 5 GB each |
| Downloads and Desktop | Highly variable |
Applications themselves are shared, which is the good news: installing an app once serves everyone. Everything the app writes per user is duplicated.
The Shared folder, and what it does not do
/Users/Shared is a folder everyone can read and write, which is useful for handing files between accounts. It does not deduplicate anything, and a file copied from it into two home folders is two files. On APFS, a copy made within the same volume is a clone that costs nothing until edited, which is the closest thing to sharing space you get.
Practical arrangements
- Keep one photo library in a shared location rather than one per person, if the household agrees.
- Use one account for media and downloads, rather than each person keeping their own copies.
- Check for accounts nobody uses, which is one of the largest things that can hide on a Mac.
- Give each person the monthly routine rather than doing it for them.
Common questions
How do I see how much space another user is using on a Mac?
From an administrator account, run sudo du -sh /Users/* which totals each home folder. It shows sizes without exposing the contents of another person's account.
Do multiple accounts on a Mac duplicate storage?
Applications are shared, but everything an app writes per user is duplicated: browser profiles, caches, containers, mail and photo libraries. Two heavy users can double most of the non application storage.
Does the Shared folder save space on a Mac?
Not by itself. It is a place everyone can read and write, but copying a file out of it into two accounts creates two files, unless APFS clones them within the same volume.
What is the biggest storage problem on a shared Mac?
Usually an account nobody uses any more, left from a migration or a family member who has moved on. A complete home folder can be tens or hundreds of gigabytes and is invisible from your own account.