Convert a size
| Dezimal (SI) | Binär (IEC) |
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What survives RAID?
The size in the field above is treated as the capacity of a single disk.
Decimal and binary side by side: why your 4 TB drive reports 3.64 TB, what Windows and Linux actually count, and how much survives RAID.
| Dezimal (SI) | Binär (IEC) |
|---|
The size in the field above is treated as the capacity of a single disk.
It happens after every disk purchase: you bought 4 TB, the system reports 3.64 TB. No fraud and no defect — just an argument about prefixes that has been running since the 1990s. This tool puts both ways of counting side by side.
Drive, SSD and USB vendors count in decimal: 1 TB = 1,000 GB = 1,000,000,000,000 bytes. Operating systems count in binary, because storage is organised in powers of two: 1024 bytes = 1 KiB. That turns 4,000,000,000,000 bytes into 3.64 TiB. The value is identical, only the divisor differs: 1 TiB equals 1.0995 TB.
Since IEC 80000-13 (adopted by NIST) decimal prefixes (kB, MB, GB, TB) mean powers of ten, while binary prefixes (KiB, MiB, GiB, TiB) mean powers of two. Calling 1024 bytes a "kilobyte" is therefore wrong by the standard — yet it survives in countless displays. We show both columns so you can quote the right one in a ticket or a datasheet.
Windows shows the binary number and still calls it "TB" — which is why the 4 TB drive appears as "3.63 TB" in Explorer. Linux is split, and the man pages are explicit: df -h and ls -lh use powers of 1024 (binary), while df -H and ls -lh --si use powers of 1000. The same disk reads "3.6T" or "4.0T" depending on the flag. Tools like lsblk, fdisk -l and smartctl report raw byte sizes — no ambiguity there.
Networking and interfaces count in bits: 8 bits = 1 byte. A gigabit link (1 Gbit/s) therefore moves 125 MB/s in theory, a 10-gigabit card 1.25 GB/s. PCIe, SATA and USB speeds are decimal in bits as well — compare those to file sizes in GiB and you get the maths wrong in two places at once.
RAID costs capacity on top: RAID 5 gives up one disk to parity, RAID 6 two, RAID 10 half of them. And the filesystem takes more — ext4 reserves 5 % for root by default, a ZFS pool with parity needs room for metadata, snapshots and slop. The RAID bridge below applies the size from the input field to the array, so "6 × 4 TB in RAID 6" becomes "16 TB usable = 14.55 TiB" right away.
You bought a drive or SSD and the vendor figure does not match what the file manager reports.
An SSD is sold as "960 GB" and reports 894 GiB — same pattern, different size class.
Sizing a backup target: "is a 20 TB drive enough for an 18 TiB repository?"
Comparing throughput: 500 MB/s read against a 4 Gbit/s link — does that add up?
Capacity planning for a RAID array or ZFS pool, including what actually remains usable.
No. All 4,000,000,000,000 bytes are there. Displayed in binary units that is 3.64 TiB. Only when a checksum tool sees fewer bytes than the datasheet promises is something actually wrong.
Because round decimal numbers sell better. A 960 GB SSD equals 894 GiB, a 1 TB SSD equals 931 GiB — the difference is the overhead for controller reserve and wear levelling, which SSD capacities account for.
No, and this is the most common mix-up. RAM is counted and labelled in binary: 16 GiB. Mass storage is sold in decimal. So "16 GB RAM" usually means 16 GiB, while "16 GB SSD" is only 14.9 GiB.
In bytes internally, but it prints the bit values too, because networks and interfaces need them. Everything is computed in your browser — nothing is sent to a server.
Standards: IEC on binary prefixes and NIST on binary prefixes. On our blog: the number worlds of an admin, understanding drive performance, RAID in practice and ZFS in practice.
💾 Capacity sorted? Continue with the matching tool: the RAID calculator for array capacity, the IOPS calculator for performance, or the download time calculator when transfer speed is the question.