Bytes, KB, MB, GB and TB Explained

Digital storage is measured in bytes, and the further units built from them (kilobytes, megabytes, gigabytes, and terabytes) are everywhere, from phone storage to broadband speeds. They’re also a common source of confusion, partly because “kilo,” “mega,” and “giga” are defined two different ways depending on the context.

What Is a Byte?

The smallest unit of digital data is a bit, which holds a single 0 or 1. Bytes are the next step up:

A byte is the common baseline unit for measuring data. For example, one character of plain text typically takes up one byte.

Understanding KB, MB, GB and TB

• Kilobyte (KB): roughly a short text document or email.
• Megabyte (MB): roughly a photo or a song.
• Gigabyte (GB): roughly a movie or a large app.
• Terabyte (TB): roughly a large hard drive or an extensive media collection.

Decimal vs Binary Storage Units

This is the part that trips people up: “kilo,” “mega,” and “giga” are defined two different ways.

Decimal prefixes (the formal SI definition, and the one storage manufacturers use):

Binary prefixes (used because computers naturally work in powers of two, and formally named KiB/MiB/GiB/TiB to distinguish them):

Software and operating systems don’t all follow the same convention: some correctly use KiB/MiB/GiB, while others display binary-calculated values but label them “KB/MB/GB” anyway, which is exactly where the confusion comes from.

Why Does Storage Capacity Sometimes Look Different?

This explains a common source of confusion: a drive sold as “1 TB” uses the decimal definition, meaning exactly 1,000,000,000,000 bytes. Many operating systems, however, calculate displayed storage using binary math while still labeling it “GB.” That same drive, measured that way, works out to about 931 “GB” (more precisely, GiB) on screen.

No storage has actually gone missing; it’s the same physical bytes, just measured against two different conventions for what “giga” means. (A small amount of a drive’s capacity is also used by the filesystem itself for bookkeeping, but the decimal-versus-binary mismatch is the main reason the numbers don’t match.)

Common Digital Storage Examples

These are rough, illustrative figures only. Actual file sizes vary significantly depending on format, compression, resolution, and quality settings: a heavily compressed photo and an uncompressed one of the same subject can differ by several times in size. If you’re comparing video files specifically, resolution plays a large role in file size, and the Digital Resolution Converter can help make sense of common resolution names like 1080p and 4K.

How to Convert Digital Storage Units

Converting between storage units means multiplying or dividing by 1,000 (decimal) or 1,024 (binary) per step, depending on which convention applies.

Example (decimal): Convert 2,500 MB to GB: 2,500 ÷ 1,000 = 2.5 GB.

Common Storage Conversion Mistakes

• Confusing bits and bytes. Internet speeds are usually advertised in megabits per second (Mbps), not megabytes, so a “100 Mbps” connection transfers roughly 12.5 MB per second, not 100 MB.
• Confusing KB and KiB. They’re close but not identical, and the gap grows at larger scales: by the gigabyte/gibibyte level, the difference is nearly 7%.
• Assuming all systems use 1,024. Storage manufacturers generally use the decimal (1,000-based) definition, while operating systems often use binary (1,024-based) math internally, even when the on-screen label just says “GB.”
• Assuming file sizes are fixed. The “same” photo, song, or video can vary enormously in size depending on compression and quality settings.

Use the Data Storage Converter

The Data Storage Converter converts between bits, bytes, KB, MB, GB, TB, and their binary KiB/MiB/GiB/TiB equivalents, so you don’t need to track which convention applies by hand.