Raw vs Usable Capacity
Also known as: raw vs usable storage, usable capacity, raw vs usable capacity, why is my phone smaller than advertised
Raw capacity is the total flash a device physically contains; usable capacity is what you can actually store after the OS, file-system overhead, reserved blocks, and decimal-vs-binary counting are subtracted. That gap is why a "128 GB" phone shows noticeably less free space.
- Decimal-vs-binary counting alone makes a 128 GB device read as roughly 119 GiB before any OS is installed.
- File-system metadata, journaling, and reserved/spare blocks for wear-leveling consume raw capacity that users never see.
- Usable capacity is the actionable figure; a cleaner can only enlarge free space within it, not change raw chip size.
Where the missing gigabytes go
Several deductions separate the number on the box from the number in Settings. First, the operating system and preinstalled apps occupy several gigabytes that can never be empty on a working device. Second, the file system itself (APFS, ext4, f2fs) reserves space for metadata, journaling, and inodes. Third, storage vendors count in decimal (1 GB = 1,000,000,000 bytes) while the OS often reports in binary (1 GiB = 1,073,741,824 bytes), so a drive sold as 128 GB is only about 119 GiB before anything is installed — roughly a 7% "shrink" from units alone.
Flash media also keeps reserved/spare blocks that the controller sets aside for wear-leveling and to replace failed cells (over-provisioning). This area is part of the raw NAND but is invisible to the user, which is another reason raw chip capacity always exceeds the usable figure.
Raw vs usable, defined
Raw capacity is the total physical storage on the NAND/UFS/eMMC die before any formatting or reservation. Usable (formatted) capacity is what the file system exposes to apps and the user after overhead, reservations, and unit conversion. The OS's "free space" figure is usable capacity minus everything currently stored — and on iOS it is further muddied by purgeable space that the system can reclaim on demand but still counts as in-use.
This is the same phenomenon as an SSD or USB stick reading smaller than advertised; it is not a defect or a manufacturer cheating, but the predictable sum of binary units plus file-system and reserved overhead.
Why it matters for cleanup
Because a chunk of capacity is permanently unavailable, the *usable* free space is the only number you can actually act on — and it fills up faster than people expect. A cleaner cannot grow raw capacity, but it maximizes usable free space by removing junk files, app cache, duplicate photos, large videos, and stale downloads. Cleanor reports against real usable capacity so the space it recovers reflects what you can genuinely reuse.