01 The short version
Use GrandPerspective when you don't know what's eating
your disk. It draws every file on the volume as a
rectangle sized by its bytes, so the thing you forgot about —
an old VM image, a caches folder nobody cleaned, a decade of
iOS backups — shows up as one big block you can't miss.
Use OmniDiskSweeper when you already know roughly where
the problem is. It skips the picture and gives you a
column of folders sorted biggest-first, and you drill down until
you find the thing and delete it. For "I know it's somewhere in
my home folder," that's faster than any treemap.
Both are genuinely free. Neither will nag you. If you only take
one line away: picture for discovery, list for cleanup.
03 Pick GrandPerspective if…
You want to see the disk. The treemap is the whole
point: proportion is instant in a way a list of numbers never
is, and "why is that rectangle a third of my drive" is a
question that answers itself. It's open source under the GPL, so
you can read exactly what it does before you point it at your
home folder. It runs on Intel Macs and on macOS versions going
back many years. And it's still actively maintained, which is
remarkable for a tool this old.
It's also the right answer for anyone who wants a free tool and
is done reading comparison pages. It has earned its reputation.
04 Pick OmniDiskSweeper if…
You want the biggest folder, right now, with no ceremony. It
opens, it scans, it shows a Finder-like column of folders sorted
by size, and you keep clicking into the biggest one until you
hit the offender. There's nothing to learn. On a machine that's
already at "your disk is almost full," that directness is worth
more than any visualization.
It's from The Omni Group, it's free with no paid tier, and it
still runs fine. It hasn't had meaningful feature work in years,
but it doesn't need any — it does one job and finished
doing it a long time ago.
05 Where both come up short
Both predate APFS, and it shows in the one place it hurts: the
numbers. GrandPerspective reports logical size,
which counts an APFS clone at full size even though it shares
every byte with the original. OmniDiskSweeper reports
size on disk, which is closer to the truth, but
neither app deduplicates clones and hardlinks across a scan.
That's the reason a folder can read 80 GB, and deleting it
gives you 12 GB back. Nothing is broken; the tool is
answering a slightly different question than the one you're
asking, and it can't tell you that. We wrote up the whole
problem in
counting bytes, and
it's the reason
"disk full but space available"
is such a common Mac complaint.
Neither app has Quick Look either, so identifying a mystery
4 GB file means switching to Finder to look at it.
Our honest recommendation
On an Intel Mac, on an older macOS, or if you want free and
open source: GrandPerspective. It's a good
app and we'd use it.
If you just want the biggest folder gone in the next two
minutes: OmniDiskSweeper. Still free, still
works.
If you're on Apple Silicon with macOS 26 and the honest
numbers matter — on-disk next to logical, clones counted
once — that's the gap Delve was built
for, and it gives you the treemap and the sorted list in one
window. $4.99 with a 14-day free trial, so it costs nothing
to find out.