Data Size Converter

Decimal vs binary data sizes

Data size has two unit families that look alike and cause endless confusion. Decimal units (KB, MB, GB) are powers of 1000. Binary units (KiB, MiB, GiB) are powers of 1024. A kilobyte is 1000 bytes; a kibibyte is 1024. The gap compounds: a "1 TB" drive holds about 931 GiB as the OS counts it, which is why a new disk looks smaller than advertised.

Who uses which

Storage vendors advertise in decimal, so a drive labeled 500 GB is 500,000,000,000 bytes. Operating systems often report in binary while using the decimal abbreviation, which is the root of the apparent shortfall. RAM is always binary. Network speeds are usually decimal, and in bits, not bytes.

Example

1 KB  = 1000 bytes
1 KiB = 1024 bytes

1 GB  = 1,000,000,000 bytes
1 GiB = 1,073,741,824 bytes

"1 TB" drive -> ~0.909 TiB

Bits vs bytes

A byte is 8 bits. Network throughput is quoted in bits per second (Mbps), while file sizes are in bytes, so a 100 Mbps link transfers about 12.5 MB per second at best. Mixing the two is a classic off-by-8 error. For converting the underlying number between bases, the number base converter helps.

FAQ

Why does my 1 TB drive show as 931 GB? The drive is 1 trillion decimal bytes, but the OS divides by 1024 three times and labels the binary result with a decimal abbreviation.

Is KB the same as KiB? Strictly no: 1000 vs 1024 bytes. Casually people use KB for both, which is exactly where the ambiguity comes from.

Why is my download slower than my connection speed? Speed is in bits, downloads in bytes; divide the advertised rate by 8, then subtract overhead.