Data Size & Bandwidth Converter

about this tool

One subject, one confusion

Every question about data sizes comes down to one thing: the same three letters mean two different amounts. In the SI prefixes, kilo is 1000, so 1 kB is 1000 bytes and 1 GB is 1 000 000 000. In the binary prefixes the standards introduced to end the argument, kibi is 1024, so 1 KiB is 1024 bytes and 1 GiB is 1 073 741 824. Drive makers, network engineers, macOS and Linux use the first; Windows uses the second but keeps the old labels, so it calls a GiB a GB.

This tool keeps everything in bytes and labels each figure by the system that produced it. A typed unit is read with its exact meaning: kB (small k) is always 1000, KiB is always 1024, and a bare KB, MB or GB follows the setting at the top, since only you know which convention your source meant. A capital K without the i is read as 1024, because the SI prefix for a thousand is a small k and a capital one only exists in the binary convention.

Bits and bytes are told apart by case, as the standards do: b is a bit, B a byte, so 100 Mb is 12.5 MB.

The missing gigabytes

Type a drive's advertised size and the tool shows what Windows will report and by how much it falls short: a 1 TB drive shows as 931.3 GiB, 6.87 % less, because 1000³ is 6.87 % smaller than 1024³. At the TiB level the gap would be 9.05 %, but no system shows a 1 TB drive in TiB, so the figure follows the unit that is actually displayed. Nothing has been lost; two systems share a label.

Speeds and transfer times

Links are sold in bits per second and downloads are shown in bytes per second, a factor of eight apart. The speed field reads both spellings — 100 Mbps, 12.5 MB/s, 1 Gbit/s, 2 MiB/s — and shows the rate in every unit, with how much it moves in an hour. Transfer time is size ÷ speed, with a line efficiency setting because real transfers never reach the line rate: TCP acknowledgements, headers and encryption take five to fifteen percent, more on Wi-Fi. At 100 %, the page suggests trying 90 %.

Limits

Sizes are Numbers, exact to about fifteen significant figures: beyond roughly 9 PB expressed in bits the last digits are approximate, which no figure shown at six significant figures reveals. Kibibits (Kib) are not offered; they exist in the standard and nowhere in practice. The efficiency setting is a single percentage; it does not model latency, congestion or the slow start of a connection, so a short transfer will take longer than the arithmetic suggests.

For the other kinds of conversion — length, weight, temperature — use the unit converter. Since the confusion here is powers of two against powers of ten, the number base converter is worth a look if the binary side is unfamiliar.

questions

Why does my 1 TB drive show 931 GB?

The drive holds a full 1 000 000 000 000 bytes. Windows divides by 1024 three times instead of 1000 and gets 931.3, then labels it GB even though the correct name for a 1024-based gigabyte is GiB. Nothing is missing; two systems are using one label. macOS and Linux count in 1000s and show 1 TB.

What is the difference between Mbps and MB/s?

A factor of eight. Network speeds are sold in megabits per second (Mbps, small b); download managers show megabytes per second (MB/s, capital B), and a byte is eight bits. A 100 Mbps line delivers at most 12.5 MB/s, and in practice five to fifteen percent less once protocol overhead is paid.

Is KB 1000 or 1024 bytes?

It depends who wrote it, which is the whole problem. The SI prefix k means 1000, and the international standard spells the 1024 unit KiB. Windows and much older software use KB to mean 1024. This tool reads kB (small k) as 1000 always, KiB as 1024 always, and lets you choose what a bare KB, MB or GB means.

What does the line efficiency setting do?

Real transfers never reach the line rate: TCP acknowledgements, packet headers and encryption take a share, typically five to fifteen percent, more on Wi-Fi. Setting 90% divides the usable speed accordingly, which gives an estimate closer to what a download dialog will show.

How large a file can this handle?

Anything you would meet: up to exabytes, with about fifteen significant figures. Beyond roughly 9 petabytes expressed in bits, JavaScript numbers lose exactness in the last digits, which does not affect any figure shown to six significant figures.