File Size Calculator: Convert Between Bits, Bytes & Other Units

Type a number into the input field and select its unit from the dropdown—options range from bits and bytes through kilobytes, megabytes, gigabytes, terabytes, and beyond to exabytes. Toggle the base switch: choose binary (1 024) to match how Windows and most operating systems report file and drive sizes, or decimal (1 000) to match storage vendor labels and ISP data caps. The result appears instantly in every other unit so you can read off whichever conversion you need without manual arithmetic. Use binary mode when checking why a drive appears smaller than advertised, or decimal mode when comparing a file against an email attachment limit or cloud storage quota.

Enter a file size and choose the unit, bits, bytes, or any of the larger prefixes (KB through EB). The result appears in every other unit as you type. Switch to binary (1024) when you want the same convention as Windows and most file managers, or decimal (1000) when you’re comparing to storage specs or data caps. The Information Hub below the calculator shows how the conversion is derived and a reference table of common media sizes.

File size is in bytes (and units built on bytes). Speeds are in bits per second. Mbps, Gbps. One byte is 8 bits, so $\text{bytes} = \frac{\text{bits}}{8}$ and $\text{bits} = 8 \times \text{bytes}$. Confusing the two is easy: a 100 Mbps link moves 12.5 MB per second, not 100 MB/s.

In binary (IEC), each step is 1024: 1 KiB = 1024 B, 1 MiB = 1024 KiB, 1 GiB = 1024 MiB. So 1 GiB = $1024^3$ = 1,073,741,824 bytes. In decimal (SI), each step is 1000: 1 KB = 1000 B, 1 MB = 1000 KB, 1 GB = 1000 MB, so 1 GB = $1000^3$ = 1,000,000,000 bytes. A drive sold as "1 TB" holds $10^{12}$ bytes; in Windows (binary) that shows as about 931 GiB. The calculator’s base toggle lets you match whichever convention you’re working with.

In the Information Hub under the calculator you’ll find a Common media and storage sizes table, floppy, CD, DVD, Blu-ray, typical MP3 and video, as a ballpark. Use the tool to convert any of those into bits, bytes, or another unit. For email, 10–25 MB is a safe attachment limit on most providers; for anything bigger, share a link from cloud storage instead.

Maximum file size depends on the file system. FAT32 limits a single file to $2^{32}-1$ bytes (4 GB minus 1 byte). NTFS and exFAT support far larger files, up to 16 EB in current specs. When moving or creating very large files (e.g. video, disk images), make sure the destination volume uses a file system that supports that size.