Storage Unit Converter

Converts across every digital storage unit, bits up to zettabytes, without the rounding drift you get doing it by hand. Comes up constantly when you're sizing a backup, comparing drive specs, or trying to work out why your "1TB" drive shows less than that in Windows.

The two systems, and why they disagree

Everything starts from bits — eight of them make a byte — and from there, two competing systems exist. Drive manufacturers use decimal (SI): 1 KB = 1,000 bytes, 1 GB = 1,000,000,000 bytes. Operating systems use binary (IEC): 1 KiB = 1,024 bytes, 1 GiB = 1,073,741,824 bytes. That mismatch is exactly why a drive sold as "1TB" shows up as roughly 931 GiB in Windows — nothing's missing, nobody's been shortchanged, it's just two different counting systems reporting the same physical capacity.

Quick reference

• 1 GB = 1,000 MB (decimal) or 1,024 MiB (binary)
• 1 TB = 1,000 GB
• 1 PB = 1,000 TB — the scale you start hearing about once you're talking data centre storage
• 1 EB = 1,000 PB — the unit the big cloud providers use when they talk about total capacity

Where this actually matters day to day

Sysadmins sizing a RAID array against a backup target, DevOps engineers provisioning cloud volumes that bill in decimal but get reported in binary by the OS, and anyone reconciling "how much space do I actually need" against "how much space does the spec sheet say I'm getting" — all the same underlying confusion, just showing up in different jobs. Once you know it's decimal vs. binary and not a manufacturing defect or a billing error, the gap stops being mysterious and just becomes a conversion you do without thinking about it.