Data Size Converter.
Enter a size in any unit and see it in all of them — both the decimal units marketing uses (KB, MB, GB = powers of 1000) and the binary units your OS actually counts in (KiB, MiB, GiB = powers of 1024). Everything runs in your browser.
Decimal (×1000)
Binary (×1024)
Why 1 GB ≠ 1 GiB.
There are two competing definitions of "kilobyte." The decimal (SI) one uses powers of 1000: 1 KB = 1000 B, 1 MB = 1,000,000 B. The binary one uses powers of 1024 — natural for computers, since memory is addressed in powers of two — and since 1998 has its own names: 1 KiB = 1024 B, 1 MiB = 1,048,576 B.
The gap grows with scale: a "1 TB" drive (10¹² bytes) shows up as about 931 GiB in an OS that counts in 1024s — which is why a new disk always looks smaller than the box promised. Storage and networking vendors use decimal; most operating systems report binary while labeling it GB, which is the root of the confusion.
This converter shows both side by side so you can see exactly what a number means under each convention. Nothing is uploaded.