Why Your 1 TB Drive Shows as 931 GB

Nothing was taken

A 1 TB drive holds 1,000,000,000,000 bytes — exactly what it says on the box.

Windows divides that by 1,024³ instead of 1,000³:

1,000,000,000,000 ÷ 1,073,741,824 = 931.32

…and prints "931 GB".

The same bytes, divided by a different number, given the same name. The standard name for what Windows is showing is GiB. If it printed that, this question wouldn't exist.

Two systems, both correct

Decimal (SI) — what drives are sold in, and how kilo/mega/giga/tera work everywhere else in measurement:

Binary — the natural units inside a machine, which addresses memory in powers of two:

Both are right. The problem is that Windows computes in the second and labels with the first.

So who's wrong?

Neither, at the arithmetic. But only one is misusing the label.

Manufacturers use the SI prefixes in their ordinary sense of thousands. Windows uses powers of two — genuinely the natural unit inside a computer — and then writes the decimal names on the result.

macOS and most Linux file managers use decimal units and label them decimally, so the same physical drive reads as 1 TB there and 931 GB on Windows. Neither machine is wrong and the drive didn't change.

Why you only notice it on drives

Because it compounds with every prefix. And it's worth stating both ways, because they're different numbers:

A text file loses nothing worth seeing.

A 4 TB drive is 4,000 GB decimal and shows as about 3,725 in Windows — an apparent shortfall of roughly 275 "GB". Which looks like a scandal and is a division.

KiB, MiB, GiB

The standard names for the binary units — kibibyte, mebibyte, gibibyte — introduced precisely to end this by giving the powers of two their own labels.

Some software uses them consistently. A great deal more ignores them, Windows included.

When you see them you can trust them completely. When you see plain "GB" you have to know which program wrote it. That's the entire practical problem in one sentence.

RAM is the exception, and it goes the other way

Memory is genuinely manufactured and sold in powers of two, so 16 GB of RAM really is 16 GiB.

It's one of the few places where the marketing figure is the binary one — and it's why RAM never produces the "smaller than advertised" complaint that storage does.

If you're checking whether a machine has what it was sold with, memory and storage need checking differently.

The eight-times trap, which is bigger

Network speeds are quoted in bits, not bytes. There are 8 bits in a byte.

A 100 Mbps connection carries at most about 12.5 MB per second — so a 1 GB download takes at least 80 seconds even at full speed.

Lowercase b is bits. Uppercase B is bytes. One character, a factor of eight, and it's easy to miss in print. That's why the converter shows a megabits output too.

Print the units reference — both systems, the compounding table, and the two exceptions people trip over.