File size converter

Why 1 MB is not always 1 MB

File sizes look simple until you compare two programs and get different numbers for the same file. The reason is that there are two conventions. In the decimal system used by disk manufacturers, networks and many operating systems, a kilobyte is 1,000 bytes, a megabyte 1,000 kilobytes, and so on. In the binary system used by memory and some operating systems, the unit is 1,024, and the correct names are kibibyte (KiB), mebibyte (MiB) and gibibyte (GiB). A "500 GB" drive holds 500 billion bytes, which a system counting in binary shows as about 465 GiB, and that difference is why the drive seems smaller than advertised.

What the converter shows

Enter a size in any of the units and you get it in all of them, decimal and binary, with the total in bits. The two systems are labelled so you can see which is which: KB, MB, GB, TB and PB are decimal, KiB, MiB, GiB, TiB and PiB are binary. A lowercase "b", as in Mb, means bits rather than bytes, and eight bits make a byte, a distinction that matters for internet speeds.

Megabits and megabytes

Internet providers advertise speed in megabits per second (Mbps), while files are measured in megabytes. A 100 Mbps connection moves at most 12.5 megabytes per second, since 100 divided by 8 is 12.5. That is why a large download seems slower than the headline speed. Enter your connection speed and the tool estimates the time a file would take in perfect conditions.

Practical uses

Checking whether a file fits a limit on an upload form or an email attachment, planning storage for photos and video, comparing the size a program reports with what a website says, estimating a download, or reading a spec sheet that mixes units. When a form says "maximum 2 MB", it is worth knowing whether it means 2,000,000 or 2,097,152 bytes: the difference is nearly five percent.

What it does not do

The time estimate assumes the full nominal speed and ignores overhead, distance, congestion and the limits of the server, so real transfers are slower. The tool does not measure your connection or the size of an actual file. To reduce a file to a limit, use the image size reducer.