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What are kilobytes (Kb), megabytes (Mb) and gigabytes (Gb)?

Jason Morrell

by Jason Morrell 
February 9, 2021

If you are new to computers, you may hear terms like kilobytes, megabytes and gigabytes. If that sounds like a foreign language to you then here is a quick run-down.


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1. Units of measure

Computers work with a unit of measure called bytes

This measure is most commonly used when describing the size of a storage media.

For example, when you visit your local computer store, the spec sheet for each computer will list RAM (computer memory) as 4, 8, 16 or 32 Gb (gigabytes) and the HDD (hard disk drive) or SSD (solid state drive) as 128, 256, 512 or 1,024 Gb. 

  • A kilobyte (Kb) is 1,024 bytes.
  • A megabyte (Mb) is 1,024 Kb (or 1,048,576 bytes).
  • A gigabyte (Gb) is 1,024 Mb.
  • A terabyte (Tb) is 1,024 Gb
  • A petabyte (Pb) is 1,024 Tb

Computers work in powers of 2.

For example, 2 to the power of 2 (2 squared) is 4 (2 x 2).

And 2 to the power of 3 (2 cubed) is 8 (2 x 2 x 2).

Keep multiplying by 2 and you get 16, 32, 64, 128, 256, 512, 1,024, 2,048, 4,096, 8,192 etc.

Hang around computers for long enough and you' ll start to spot these figures.

As a beginner, this doesn’t mean anything without a context. So let me give you some examples (these figures are approximate).

2. Examples of size and capacity

  • A CD holds around 720Mb of data. You can fit every Beatles song on one CD!
  • A DVD holds around 4.5Gb of data.
  • A 4-minute song downloaded from iTunes is 4Mb (250 songs per Gb).
  • A typical webpage is 3Mb (according to SpeedCurve, 2017).
  • A 2 hour movie from Netflix is 500Mb (standard def) or 1Tb (high def).
  • The smallest hard disk drive (HDD) or solid state drive (SSD) you can buy is 128Gb. The Windows operating system uses about 20Gb leaving over 100Gb for your stuff.


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I hope you found plenty of value in this post. I'd love to hear your biggest takeaway in the comments below together with any questions you may have.

Have a fantastic day.

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About Jason Morrell

About the author

Jason Morrell

Jason Morrell is a professional trainer, consultant and course creator who lives on the glorious Gold Coast in Queensland, Australia.

He helps people of all levels unleash and leverage the power contained within Microsoft Office by delivering training, troubleshooting services and taking on client projects. He loves to simplify tricky concepts and provide helpful, proven, actionable advice that can be implemented for quick results.

Purely for amusement he sometimes talks about himself in the third person.


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