Disk Usable Capacity Calculator – Formatted vs Raw
Calculate formatted usable capacity after filesystem overhead.
About This Calculator
Calculate formatted usable capacity after filesystem overhead. Use the calculator above for instant results.
Worked Examples
- Formatted: 950 GB | OS shows: ~893 GiB
- Manufacturer 1000 GB - overhead = ~931 GiB to OS - 5% NTFS = 884 GiB
Answer: ~950 GB / ~884 GiB
- Formatted: 3,800 GB | OS shows: ~3,539 GiB
Answer: ~3,539 GiB usable
- Formatted: 481 GB | 6% overhead for FAT32
Answer: ~481 GB
Who Uses This Calculator?
Plan actual usable storage.
Understand why drives show less space.
Filesystem capacity planning.
Data center capacity planning.
Common Mistakes to Avoid
❌ Manufacturer GB vs OS GiB
1 TB drive = 1,000,000,000,000 bytes. Windows shows in GiB (1 GiB = 1,073,741,824 bytes) = 931 GiB. Not a scam.
❌ Filesystem overhead
Journaling, metadata, and reserved blocks take 5-10% typically. ext4 reserves 5% for root by default.
Frequently Asked Questions
Why does my 1 TB drive show 931 GB in Windows?
Windows (and Linux) report in GiB but label it 'GB'. 1 TB manufacturer = 931 GiB. Not missing space.
Reduce filesystem overhead?
On Linux, tune ext4 reserved blocks: tune2fs -m 1 /dev/sda1 (reduces from 5% to 1% reserved).
SSD vs HDD overhead?
SSDs have additional OP (over-provisioning) — typically 7-15% of raw NAND not shown in capacity. Needed for wear leveling.