Comparison

MB vs GB vs TB

The three data-storage tiers everyone meets — and how SI decimal differs from binary IEC units.

Megabyte (MB)Gigabyte (GB)Terabyte (TB)
SI decimal10⁶ = 1,000,000 B10⁹ B10¹² B
Binary (IEC)MiB = 2²⁰ ≈ 1.049 MBGiB = 2³⁰ ≈ 1.074 GBTiB = 2⁴⁰ ≈ 1.1 TB
Typical usePhoto, MP3HD movie, OS installDrive, cloud bucket
1 of the next1,000 MB = 1 GB1,000 GB = 1 TB—
Megabyte (MB) pros
  • Matches consumer file sizes
  • Easy mental math
Gigabyte (GB) pros
  • Standard SaaS pricing tier
  • Default unit for SSDs

When to use which

Use Megabyte (MB)

Use MB for individual files and email attachments.

Use Gigabyte (GB)

Use GB for OS, application installs, RAM sizing, and cloud storage budgets.

Historical context

The confusion here is not historical accident but an unresolved disagreement. Every other use of the prefix kilo means a thousand, but early computing borrowed it for 1,024, which is 2¹⁰ and the number that falls naturally out of binary addressing. For small numbers the discrepancy hardly showed. It compounds with every step up the scale, so by the terabyte the two readings are nearly 10% apart. In 1998 the IEC proposed separate binary prefixes — kibi, mebi, gibi and tebi, written KiB, MiB, GiB and TiB — to end the ambiguity. Adoption has been partial at best. Drive manufacturers use decimal units, so a one-terabyte drive really does hold 10¹² bytes. Windows reports the same drive in binary units while still labelling them GB, which is why it shows about 931 GB and why buyers have periodically accused manufacturers of shorting them. macOS and Linux have largely moved to decimal reporting, which is why the same drive can read differently on two machines.

Practical recommendation

Assume decimal units — powers of a thousand — unless you are reading Windows storage figures or memory sizes, both of which are binary. RAM is the reliable exception: it is addressed in binary and always quoted that way, so 16 GB of memory really is 16 GiB. When precision matters, write KiB, MiB and GiB explicitly rather than trusting the reader to guess. And expect the gap when buying storage: a decimal gigabyte is 6.87% smaller than a gibibyte, which is the whole of the missing space people complain about.

Related tools

Data storage converterData transfer formula

FAQs

Why does my 1 TB drive show 931 GB?+

Drive makers use SI TB (10¹² bytes); operating systems display in TiB (2⁴⁰ bytes), which is ~9.1% smaller.

Is RAM measured in GiB or GB?+

RAM is universally GiB (binary). 16 GB RAM is actually 16 GiB ≈ 17.18 GB in decimal.

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