How to Use This Tool
You buy a 1 TB drive, plug it in, and the computer reports 931 GB. Roughly 70 gigabytes appear to have vanished. Nothing has: the drive holds exactly what the box promised, and the two numbers differ because the manufacturer and the operating system divide by different amounts. This converter shows both answers at once so you can stop wondering which is right. They both are.
The two conventions
The decimal convention, used by the SI system, treats each step as a factor of 1,000. A megabyte is a million bytes and a terabyte is a trillion. Storage manufacturers, network equipment and most Linux command-line tools use this, and it is the one the international standard actually defines.
The binary convention steps by 1,024, because computer memory is addressed in powers of two. Windows File Explorer, macOS in some contexts, and most RAM specifications use this. The correct names for these units are kibibyte, mebibyte and gibibyte — KiB, MiB, GiB — but almost nobody outside standards documents uses them, which is exactly why the confusion persists.
The gap compounds. At the kilobyte level it is 2.4%. At megabytes it is 4.9%, at gigabytes 7.4%, and at terabytes almost 10%. That is why nobody argues about a floppy disk and everybody notices on a 4 TB drive.
Using the converter
Enter an amount and choose the source and target units. The toggle switches the working divisor between 1,000 and 1,024, and the panel below always shows both results side by side with the difference expressed as a percentage. The table lists your value in every unit from bits to petabytes, which is useful when a spec sheet quotes gigabits and your storage quote is in gigabytes — a factor-of-eight difference that causes more procurement mistakes than the 1000-versus-1024 question ever has.
Which one should you use?
- Buying storage: decimal. The box uses it, and you will get exactly what it says in bytes.
- Reading Windows disk usage: binary, even though Windows labels it "GB".
- Sizing RAM: binary, always. Memory really is manufactured in powers of two.
- Network speeds: decimal, and in bits. A 100 Mbps connection transfers about 12.5 MB per second at best.
- Cloud storage and egress billing: usually decimal, but check — the difference on a large monthly bill is real money.
The transfer time estimator
The box at the bottom converts your amount into a realistic transfer duration. Note that it assumes the quoted speed is sustained, which it rarely is: protocol overhead, disk seek time and contention typically cost 10–20% in practice. If a number looks optimistic, it is.
