SI vs IEC byte converter

Hard-drive boxes, SSD stickers, and cloud invoices almost always print capacity in SI decimal units: one gigabyte is exactly one billion bytes and one terabyte is one trillion. File managers on Windows, macOS, Linux, and many embedded tools count with IEC binary prefixes instead: one gibibyte is two to the thirtieth bytes and one tebibyte is two to the fortieth. That single choice is why a disk sold as one terabyte often appears as roughly nine hundred thirty-one gibibytes after formatting, and why teams argue about missing storage that was never missing—only relabeled. This SI versus IEC byte unit converter takes a finite non-negative size, a source unit, and a target unit, multiplies through an exact byte base using powers of ten or powers of two, and returns the converted value plus a manufacturer-versus-operating-system explanation when the source is a graded storage label such as GB or GiB.

Why manufacturer gigabytes disagree with operating-system gibibytes

Storage marketing follows the International System of Units for multiples of the byte: kilo means one thousand, mega means one million, giga means one billion, tera means one trillion, and so on. Under that SI decimal rule a one-terabyte drive is exactly one trillion bytes before filesystem overhead.

Operating systems and many developer tools adopted the IEC 80000-13 binary prefixes so that powers of two stay exact inside address math: a kibibyte is one thousand twenty-four bytes, a mebibyte is two to the twentieth, a gibibyte is two to the thirtieth, and a tebibyte is two to the fortieth. When the same physical byte count is shown with an SI letter on the box and an IEC letter in the UI, the printed numbers diverge even though no capacity vanished.

Roughly seven percent separates a gigabyte from a gibibyte, and nearly ten percent separates a terabyte from a tebibyte, which is large enough to trigger support tickets, capacity-planning errors, and skeptical finance reviews. This converter keeps both systems honest: send the manufacturer value in GB or TB and ask for GiB or TiB to see what a binary-aware OS should report for that raw byte count, or reverse the path when you only have the OS reading and need the SI label your vendor would print.

Optional counterpart fields on the response name the paired unit at the same grade and the percentage gap so dashboards can show both numbers without hand-waving. Filesystem metadata, reserved partitions, and RAID parity still reduce usable space further; those effects are outside pure unit conversion and should be modeled separately after the SI-versus-IEC step is correct.

Where the gap between GB and GiB matters

Use the free in-browser SI versus IEC byte unit converter when you need a quick check that a one-terabyte SSD label should appear near nine hundred thirty-one gibibytes in a file manager, that five hundred twelve gigabytes of advertised flash is about four hundred seventy-six point eight gibibytes under IEC counting, or that a container limit written as four gibibytes is four point two nine four nine six seven two nine six gigabytes if a billing tool insists on SI.

Enter the number and units, read the result and the manufacturer-versus-OS note, and copy them into a ticket or spreadsheet without installing a unit library. Results are safe to cache because the algorithm is fully deterministic.