Deleting APFS volumes or repartitioning erases data on affected volumes. Back up first.
What you will achieve
Merge free space between APFS containers on the same physical disk — or understand when you cannot.
APFS containers hold volumes that share free space pool — unlike fixed partitions. “Merging containers” usually means deleting an extra partition or Boot Camp slice and expanding the main container. There is no wizard — only backup, delete, grow.
1) APFS container model
One physical disk has one APFS Container; multiple volumes share free space dynamically. You rarely “merge containers” — you add/delete volumes inside one container.
2) Add volume instead of partition
- Disk Utility → select APFS container → + Volume.
- New volume shares pool with macOS Data — no fixed size unless quota set.
3) Delete unused volume
Select volume → Delete APFS Volume — space returns to shared pool. Cannot delete Macintosh HD system volume while booted from it.
4) Multiple containers on one disk
Rare — created by Boot Camp Assistant or manual partitioning. To merge, backup second container, delete its partition in Disk Utility (destructive), expand primary container into free space. No live merge button.
5) External disks
Repartition only with backup — repartitioning erases. Use single container with multiple volumes for flexibility.
6) Boot Camp partition removal
Removing Windows Boot Camp partition frees space — use Boot Camp Assistant to restore single macOS partition instead of manual delete when possible. Manual delete risks EFI partition misalignment.
7) Disk Utility limitations
Cannot merge two physical disks into one container — only partitions on same device. RAID via SoftRAID or hardware RAID is separate topic.
8) Quotas on volumes
APFS volume quotas reserve minimum space — deleting quota volume returns reservation to pool. Check diskutil apfs list in Terminal for detailed container map.
Verify
Disk Utility shows one container with expected free space; volumes mount; no duplicate containers unless intentional.
Additional troubleshooting notes
If steps above do not resolve the issue on the first attempt, reboot once, confirm System Settings → General → Software Update is current, and retry with a second administrator account to rule out profile or keychain corruption in your daily user. Document exact error text from Console.app with timestamp — vague “it still fails” without logs wastes support time. On Apple Silicon, re-test after full shutdown (not just restart) because firmware and Thunderbolt controllers reset only on cold boot. Intel Macs should repeat test in Safe Mode to bypass third-party login items. Before erase or keychain reset, verify Time Machine or clone backup completed — batch 3 guides assume Monterey/Ventura/Sonoma/Sequoia paths in System Settings; search Spotlight for renamed panes if your macOS version labels differ slightly.