GB to TB Converter

gigabytes to terabytes — quick reference

The formula, worked line by line

One division by a thousand, and then the far more interesting question of what the other number on your screen is counting. This page spends its length on the second part, because the first part is a decimal point and nobody has ever got it wrong.

Holding that straight makes the rest easy. Every figure below is the same physical capacity expressed against a different denominator, and once you know which denominator produced a number, the number stops being surprising.

terabytes = gigabytes / 1,000
1 TB = 1,000 GB = 1,000,000,000,000 bytes
1 TiB = 2^40 = 1,099,511,627,776 bytes
10^12 / 2^30 = 931.322574615478515625
10^12 / 2^40 = 0.909494701772928237915

Where the seven percent comes from

Each prefix step multiplies the decimal-to-binary ratio by 1.024. One step gives 2.4 percent, two 4.9, three 7.37 and four 10.0. A gigabyte is three steps above a byte, which is why the gigabyte gap is 7.37 percent, and a terabyte is four, which is why the terabyte gap is a round-sounding ten.

Capacity you genuinely do not get

That last caveat matters. Figures such as "NTFS takes 12.5 percent for its master file table" circulate widely and are wrong: the zone concerned is reserved address space that remains available for user files. If you want to know what a specific volume actually gives you, format it and read the free space, because no general percentage is reliable.

How to use the GB to TB converter

A terabyte is a thousand gigabytes, so the conversion is one decimal point. What sends people here is not the sum but the discrepancy waiting at the other end of it: a drive sold as 1 TB, which is 1,000 GB, frequently appears in software as roughly 931 GB. The arithmetic behind that number is short, exact, and worth seeing once.

A trillion bytes divided by 2^30 — that is 1,073,741,824, the number of bytes in a gibibyte — gives 931.322574615478515625. Software that performs that division and then prints the letters GB has produced a correct count of gibibytes with the wrong label attached. No capacity has gone anywhere; the ruler changed, not the drive.

Seven percent is large enough to feel like something has been taken. That perception is why the labelling has been litigated, and why drives now carry a capacity note on the box. It is not, however, evidence of a shortfall: both figures describe the same trillion bytes, and neither of them is a measurement error.

There is a second, smaller wrinkle in the other direction. Drives are not always exactly a trillion bytes. Capacity is built from 512-byte logical sectors, and one common 1 TB model specifies 1,953,525,168 of them, which comes to 1,000,204,886,016 bytes. The label is a rounded decimal figure, and the true count usually sits slightly above it.

When the label went to court

The gap has been litigated twice in California, and both cases are routinely mis-described online, so the details are worth stating carefully. Neither produced a finding that drives were short of capacity. Both were about whether the decimal definition was adequately disclosed to buyers.

What survives from both is the disclosure now printed on drives and specification pages. Seagate's wording is representative: "One gigabyte, or GB, equals one billion bytes when referring to hard drive capacity." The sentence exists because a court accepted that buyers could not otherwise be expected to know which gigabyte was meant.

Why systems disagree with each other

Different software makes different choices, and the labels do not always reveal them. Apple states that OS X Leopard and earlier reported storage in binary units, and that its systems from Snow Leopard onwards report capacity in decimal — which is why a Mac and an older machine can show different figures for the same drive.

On Linux the choice is explicit and documented: the GNU coreutils manual specifies that the human-readable flag on df uses powers of 1,024, while the alternative flag uses powers of 1,000. Nothing is hidden there, because the tool tells you which mode it is in and offers both.

For Windows the honest answer is that no clear statement from Microsoft settles it. The relevant developer documentation says one thing in its text and computes another in its own worked examples, and it describes a formatting function rather than the file manager. The behaviour is easy to observe; what is missing is an authoritative source to cite for it.

Every gigabytes value, worked out

60 common gigabytes figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask