Bytes, Kilobytes, Megabytes: The Complete Hierarchy Explained

5 min read•June 1, 2025•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

All digital data is ultimately made of bits — binary digits, each a 0 or a 1. Eight bits make a byte, and bytes stack up through a hierarchy of prefixes — kilobytes, megabytes, gigabytes, terabytes — to describe everything from text messages to data center storage.

There's a complication: the prefixes have two interpretations. In strict SI usage, 'kilo' means 1,000 (decimal). In traditional computing, 'kilo' meant 1,024 (binary, because 2¹⁰ = 1,024). Both interpretations are still in use, which is why your 500 GB hard drive shows up as about 465 GB in Windows.

The Data Storage Hierarchy

Decimal (SI, used by storage manufacturers, macOS, cloud):
  1 KB  = 1,000 bytes
  1 MB  = 1,000 KB  = 1,000,000 bytes
  1 GB  = 1,000 MB  = 1,000,000,000 bytes
  1 TB  = 1,000 GB  = 1,000,000,000,000 bytes
  1 PB  = 1,000 TB

Binary (IEC, used by RAM, Windows historically, networking):
  1 KiB = 1,024 bytes
  1 MiB = 1,024 KiB = 1,048,576 bytes
  1 GiB = 1,024 MiB = 1,073,741,824 bytes
  1 TiB = 1,024 GiB

Starting point:
  1 bit   = 0 or 1
  8 bits  = 1 byte
  1 byte  = 1 ASCII character

Where the Confusion Comes From

Early computer memory used powers of 2 for addressing. 2¹⁰ = 1,024, which is close to 1,000, so engineers called 1,024 bytes a 'kilobyte.' This was sloppy but convenient for decades. The IEC introduced proper binary prefixes in 1998: kibibyte (KiB = 1,024 bytes), mebibyte (MiB = 1,048,576 bytes), and so on. But adoption was slow.

Today, hard drive and SSD manufacturers use decimal (1 GB = 1,000,000,000 bytes), which makes their drives look bigger. Operating systems — particularly Windows — historically reported storage in binary units but labeled them GB, making the drive appear smaller. The gap grows at higher levels: a 1 TB (decimal) drive contains 909 GiB (binary), showing as about 909 GB in older Windows versions.

Practical Sizes by Unit

1 byte: a single character (the letter 'A' = 1 byte in ASCII). 1 KB: about one short text message or a paragraph of plain text. 1 MB: a typical photo from a smartphone camera in compressed JPEG format; about 1 minute of standard-quality MP3 audio. 1 GB: about 1,000 photos, or 1 hour of HD video stream, or a typical mobile game download.

1 TB: the standard size for consumer laptops and desktop hard drives. It holds roughly 250,000 photos, 500 hours of HD video, or 200,000 songs. 1 PB: the scale of large cloud providers and government archives — Google processes petabytes of search data daily.

Frequently Asked Questions

How many bytes is 1 MB?

In decimal (SI), 1 MB = 1,000,000 bytes (1 million). In binary, 1 MiB = 1,048,576 bytes. Storage manufacturers use decimal; RAM capacity is often specified in binary.

Why does my hard drive show less space than advertised?

Drive manufacturers sell in decimal GB (1 GB = 1,000,000,000 bytes). Windows historically reported in binary GiB (1 GiB = 1,073,741,824 bytes) while labeling them GB. A 500 GB drive contains 500,000,000,000 bytes = about 465 GiB — which Windows displayed as '465 GB.'

What's the difference between KB and KiB?

KB (kilobyte) officially means 1,000 bytes in SI notation. KiB (kibibyte) means 1,024 bytes in IEC binary notation. In practice, many programs and operating systems still use KB to mean 1,024 bytes, ignoring the formal distinction. Context determines which interpretation applies.

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