Data Size Conversion: Bytes, Kilobytes, Megabytes, Gigabytes & Beyond

The Two Systems: Decimal vs. Binary Prefixes

This is the most confusing thing about data units. Two different systems use the same (or similar) words to mean different things:

Decimal (SI): 1 KB = 1,000 bytes (10³). Used by hard drive manufacturers and network speed measurements. Based on powers of 10.
Binary (IEC): 1 KiB (kibibyte) = 1,024 bytes (2¹⁰). Used by operating systems (Windows, Linux) and memory (RAM) measurements. Based on powers of 2.

This is why a "1TB" hard drive shows as ~931GB in Windows — the manufacturer uses decimal terabytes (1,000,000,000,000 bytes) while Windows reports in binary gigabytes (1,073,741,824 bytes each).

Complete Data Size Reference

Decimal (SI)          Binary (IEC)
1 KB  = 10³  bytes   1 KiB = 2¹⁰ bytes = 1,024 bytes
1 MB  = 10⁶  bytes   1 MiB = 2²⁰ bytes = 1,048,576 bytes
1 GB  = 10⁹  bytes   1 GiB = 2³⁰ bytes = 1,073,741,824 bytes
1 TB  = 10¹² bytes   1 TiB = 2⁴⁰ bytes = 1,099,511,627,776 bytes
1 PB  = 10¹⁵ bytes   1 PiB = 2⁵⁰ bytes

The difference gets larger as the unit grows: at KB scale the difference is 2.4%, at GB it's 7.4%, at TB it's ~10%.

When to Use Which

Use decimal (KB, MB, GB): Network speeds (100 Mbps), storage marketing, data transfer limits, cloud storage plans.
Use binary (KiB, MiB, GiB): RAM sizes, file sizes in your OS, disk partition sizes, cache sizes.
When in doubt: Check the number. If it's a clean power-of-2 (1,024, 65,536, 1,048,576), it's probably binary. If it's a round number in base 10 (1,000, 1,000,000), it's probably decimal.

Real-World Sizes for Reference

1 byte: One ASCII character
1 KB: A short email (~1–2 KB of text)
1 MB: A high-resolution photo (~2–5 MB)
1 GB: A feature film in HD (~4–8 GB)
1 TB: A laptop hard drive. ~250,000 photos or 500 hours of HD video
1 PB: A data center's worth. Google processes ~20 PB of data per day

Convert Data Sizes Instantly

Use ToolsVito's Data Size Converter to convert between bytes, KB, MB, GB, TB, and PB — showing both decimal (SI) and binary (IEC) values side by side. Type a value and see the conversion in every unit simultaneously.