File Size Converter

Features

• Both decimal (SI) and binary (IEC) conventions side by side
• Every unit from bytes to tebibytes
• Exact byte count with no rounding
• Transfer time estimates at six connection speeds
• Explains the drive-capacity discrepancy

How to use it

1. Enter a size and pick its unit.
2. Read the decimal and binary tables.
3. Choose a connection speed for a transfer estimate.
4. Copy every representation at once.

Why your 1 TB drive shows as 931 GB

There are two competing definitions of a kilobyte and both are in active use. The decimal convention follows SI prefixes: a kilobyte is 1,000 bytes, a megabyte 1,000,000. The binary convention treats a kilobyte as 1,024 bytes, because computers address memory in powers of two and 2¹⁰ is conveniently close to 1,000.

Storage manufacturers use the decimal definition, so a drive sold as 1 TB contains 1,000,000,000,000 bytes. Windows reports capacity using the binary definition but labels it with decimal-looking units, dividing by 1024 three times and calling the result GB. That gives 931, which is why the drive appears to be missing 7% of its capacity. Nothing is actually missing, the two systems are just counting differently. macOS switched to decimal reporting in 2009, so the same drive shows as 1 TB there.

The IEC introduced unambiguous binary prefixes in 1998, kibibyte, mebibyte, gibibyte, written KiB, MiB and GiB. They are precise and largely ignored outside Linux tooling and technical documentation. Networking adds one more trap: transfer speeds are quoted in bits per second, not bytes, so a 100 Mbps connection moves at best 12.5 MB per second, and less after protocol overhead. The estimate above assumes about 90% efficiency.