TB to GB Converter

terabytes to gigabytes — quick reference

The formula, worked line by line

One multiplication by a thousand, then one optional adjustment for the scale your software counts on. Both are given below, because the first answers what you bought and the second answers what you will see.

It sounds like a hedge and is not. The two figures count the same bytes, so there is no contradiction to resolve — only a decision about which unit to do your arithmetic in. Doing it in the unit the machine uses removes the surprise.

gigabytes = terabytes x 1,000
bytes = terabytes x 1,000,000,000,000
gibibytes = terabytes x 10^12 / 2^30
1 TB = 931.322574615478515625 GiB
1 TiB = 1,099,511,627,776 bytes = 1.0995 TB

Why 931 rather than 930 or 932

The figure is exact rather than approximate. A trillion divided by 1,073,741,824 is 931.322574615478515625, and it terminates because both numbers are products of twos and fives. Any tool showing 931.32 for a labelled terabyte has done the division correctly; the only thing it got wrong was printing GB instead of GiB.

The prefixes above the terabyte

Consumer drives reach into the tens of terabytes, so most readers will not meet a petabyte on a shelf. It is worth knowing the shape of the ladder anyway, because cloud storage and archive pricing are quoted in those units and the same decimal convention applies all the way up.

How to use the TB to GB converter

One terabyte is a thousand gigabytes, which is a trillion bytes. The conversion is a decimal point, and the reason to run it is almost always planning: working out whether a drive will hold what you intend to put on it, or whether a backup will fit, or how many of something a given capacity is worth.

For that purpose there are two numbers rather than one, and it is worth deciding early which you are planning against. The label promises a thousand gigabytes. The figure your operating system displays will be nearer nine hundred and thirty-one, because it counts in units of 2^30 bytes while still writing the letters GB.

Plan against 931 and you will never be short. The nine hundred and thirty-one is not a deduction anyone has made; it is the same trillion bytes counted in larger units. But since it is the figure that appears when the drive is in front of you, it is the one that determines whether the last file fits.

Drives have carried a capacity note since the mid-2000s, when the decimal definition was litigated in California. Seagate's wording is representative: one gigabyte equals one billion bytes when referring to hard drive capacity. The note exists because a court accepted that buyers could not be expected to work out which gigabyte was meant.

Sizing a drive against what you will actually store

Capacity planning fails in a predictable way: the arithmetic is done against the label, the drive is bought, and the shortfall appears later as a percentage nobody budgeted for. Two adjustments fix it. Plan against the binary figure, and leave working room, because a filesystem near capacity behaves badly regardless of how it counts.

The twenty percent margin is a working habit rather than a rule from a specification. Filesystems fragment and slow as they approach full, snapshots and temporary files need somewhere to live, and the cost of the margin is small next to the cost of migrating everything to a larger drive earlier than planned.

What a terabyte is worth

A trillion bytes is difficult to hold in your head, so it helps to convert it into counts of things. The counts below use round per-item sizes chosen for legibility rather than measured averages, and the only honest way to use them is to substitute figures from your own files.

One further note on redundancy. In a mirrored pair of drives the usable capacity is one drive, not two, and in parity arrays it is the total less one or two members. Those reductions are far larger than any unit conversion, and they are the ones most often left out of a capacity plan.

Every terabytes value, worked out

49 common terabytes figures each get their own page, with the answer, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask