Long-lived Minecraft worlds grow: every exploration session writes new chunks to disk forever, and most of them are terrain somebody flew over once. A bloated world means slow backups, slow uploads and slow restores. MCA Selector shrinks a world in two honest ways — deleting chunks that carry no value, and defragmenting the region files — and this guide shows both, plus how to measure the result yourself.
Back up your world first: MCA Selector writes deletions and NBT changes straight to disk the moment you confirm them — there is no undo and no File → Save step to catch a mistake. Close Minecraft (and stop your server, if the world is on one), then copy the whole world folder somewhere safe before you edit.
Where world size actually lives
A Java Edition world stores its terrain in .mca region files: one file covers a 32×32-chunk region (512×512 blocks), and the Overworld, Nether (DIM-1) and End (DIM1) each keep their own set, alongside poi and entities data. World size is therefore driven by generated area: the further your players have explored in every direction — and the more dimensions they have opened — the more region files exist. There is no setting that shrinks that; you shrink it by removing area or by cleaning up the files themselves.
Method 1: Delete chunks nobody uses
The biggest wins come from chunks that were generated in passing. The recipe mirrors the reset workflow, minus the intent to revisit:
- Open the chunk filter and match chunks with a very low
InhabitedTime— terrain that was generated but barely spent time in. - Protect what matters first: build the selection of your bases and infrastructure, and use Subtraction mode (or a negated group) so the filter can never match them.
- Apply the filter as a selection and look at it on the map before deleting — low InhabitedTime is a heuristic, and small outposts hide in it.
- Export the selection as CSV for your records, then delete (Selection → Delete selected chunks). The freed space is real but the deletion is, as always, instant and permanent.
- For whole areas nobody visits — a retired mining dimension, the far side of an exploration era — select and delete them wholesale, or prune them with the pruning workflow if they should regenerate fresh later.
Method 2: Remove an unused dimension entirely
If a dimension was generated by accident or for a one-off event — a few chunks of End, a test Nether — its whole folder can be removed in your file manager with the game closed: delete the dimension’s folder (DIM-1 for the Nether, DIM1 for the End, or the dimension folder of a datapack dimension) and Minecraft generates a fresh, empty dimension on the next visit. This is a file operation, not an MCA Selector feature, and the warning is absolute: everything in that dimension — Nether hubs, tunnels, End farms — is in that folder. Check twice, back up first, and if there is anything in the dimension worth keeping, delete selectively with the tool instead.
Method 3: Defragment the region files
Deleting chunks inside a region file can leave empty sectors behind — allocated space that no longer holds data. MCA Selector’s Defragment function rewrites the region files without those gaps, compacting what remains. It does not change a single chunk’s contents; it simply stops the files from carrying the holes left by earlier deletions. Run it after a big deletion pass, on the same backup discipline as everything else in this tool.
Measure the result yourself — no magic numbers
Any honest size guide ends with measurement, not promises, because the outcome depends entirely on how much dead terrain your world carries. Before you start, note the world folder’s size on disk (folder properties in your file manager). Repeat after each method. A world that is 90% lived-in bases will barely shrink; a world with years of fly-over exploration can shrink dramatically. Beware any guide — including older versions of this website — that quotes a specific before/after size for your world: nobody can know that number but your file manager.
Verify, then enjoy the smaller backups
Open the trimmed world in Minecraft and visit your bases, farms and portals in every dimension you touched. Confirm the areas you meant to keep are untouched, then take a fresh backup of the slimmed world — the routine this whole exercise was for: smaller backups, faster server uploads, cheaper storage. Then go back to the complete guide for the rest of what the tool can do.
Download MCA Selector 2.9
Everything in this guide works with the current release. Get the Windows installer, the cross-platform .jar, the macOS .dmg or the Linux .deb/.rpm from the MCA Selector download page — every button there points at the official GitHub release files and lists the SHA-256 checksum, with a clearly labelled site mirror as a fallback.
One last backup reminder: keep the copy of your world you made before editing until you have loaded the edited world in Minecraft and confirmed it looks right. Deletions and NBT changes in MCA Selector are permanent once applied.