Convert gigabytes to gibibytes

A gigabyte (GB) is one billion bytes, or 10⁹ B. That is what the SI prefix giga means everywhere else, and it is the unit drive, memory card and phone makers use for capacity[1].

A gibibyte (GiB) is 2³⁰ bytes, or 1,073,741,824 B. In 1998 the International Electrotechnical Commission (IEC) published binary prefixes such as gibi so that a size counted in powers of 1024 would no longer share a name with one counted in powers of 1000[1]. The extra i in the symbol tells you at a glance which one you are looking at.

A gibibyte is 7.37% larger than a gigabyte, so the same capacity written in GiB is always a smaller number. For a single photo that makes no difference, but on a 1,000 GB drive the figure drops to 931.32. Terabytes follow the same pattern, and the GB to TB converter handles that step, and the TB to TiB converter gives a 4 TB drive in tebibytes.

Multiply the gigabytes by one billion to get bytes, then divide by 1,073,741,824. In one step: GiB = GB × 0.9313226.

A 500 GB SSD from a product listing is 500 × 0.9313226 = 465.66 GiB. The OCR GCSE Computer Science specification taught in schools in England defines a gigabyte as 1,000 MB, but also accepts calculations with 1,024[2]. That is why a 128 GB memory card can be 128 GB in one answer and 119.21 GiB in another, the second being the figure Windows shows. A 2,000 GB drive holds 1,862.65 GiB. The result always comes out roughly 7% lower than the number on the box.

In Excel, use =CONVERT(A2,"Gbyte","Gibyte"). In this function the prefix "Gi" stands for gibi, 2³⁰, and plain "G" stands for giga[3].

To go the other way, open the GiB to GB converter. The Swap order button takes your number there, and the data size converter covers every other pair of units.

The manufacturer counts in decimal, so a 1 TB drive holds one trillion bytes, or 1,000 GB. Seagate puts it plainly: people are often confused when a new 1 TB drive shows only about 931 GB, because the storage industry states capacity in decimal[4]. Windows divides the same number of bytes by powers of 1024 but still labels the result GB rather than GiB[5]. So This PC shows 931 GB, even though the drive holds exactly as many bytes as the label promised.

On a Mac the same drive shows 1 TB. Apple notes that OS X Leopard, iOS 10 and earlier versions reported capacity in binary[6], while current macOS reports it in decimal, as do Ubuntu and Debian[5]. If one external drive shows two different numbers on two computers, nothing is wrong with it.

A small part of the gap has a different cause. Formatting and the operating system take up some space, which is why Apple adds "actual formatted capacity less" next to the capacity of its devices[6].