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Bits and bytes explained: how to understand internet speed

Can't tell your bits from your bytes? Read on to learn the difference and figure out what broadband speed you need.
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Even though people tend to informally refer to them both as 'megs', connection speeds and data sizes are actually measured differently.

The word 'meg' could refer to two very different values: megabits and megabytes. But aren't they the same thing?

Actually no, there's a big difference between a bit and a byte. A byte is much bigger — eight times bigger, to be exact — with eight bits fitting inside every byte. So there are eight megabits (Mb) in every megabyte (MB), and eight gigabits (Gb) in every gigabyte (GB).

1 megabyte equals 8 megabits

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Bits, bytes and broadband speeds

You may be wondering how this relates to you and your broadband speed.

Data sizes are usually measured in 'bytes' (with a capital B), and broadband speeds are measured in 'bits' (lowercase b). Based on the file size and your connection speed, you can estimate how long it'll take you to download something.

files are measured in bytes, speed is measured in bits

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Let's say you find a file online that is 50 megabytes (MB) in size, and you want to download it using your 50 megabits per second (Mbps) broadband connection. This won't take one second; it will take eight times one second because a megabyte is eight times bigger than a megabit. So in theory — and with a perfectly consistent speed — it should take eight seconds to download.

Before you start reaching for your calculator, read our guide to download times. We've pulled together a list of the most common broadband speeds and file sizes to give you an idea of how long it will take to download films, TV series, songs and more.

How can I tell the difference between a bit and a byte?

From how it's written. A byte is an uppercase 'B' and a bit is a lowercase 'b'. If it says MB, all capitals, then it is a megabyte. If it says Mb, then it is a megabit.

There is one exception to this, of course, and it is the symbol for kilobit, which is 'kb', all lowercase. But these file sizes are so small nowadays that you shouldn't really see much of them.

It's easy to figure out based on common sense: an uppercase 'B' is physically larger than a lowercase 'b', and a byte is larger than a bit.

when abbreviated, megabytes has a big B, megabits has a small b

Other file sizes to know about

While there's a range of different file sizes, most of us only need to know a few different prefixes. Here are the most common ones.

  • KB, MB, GB - A kilobyte (KB) is 1,024 bytes. A megabyte (MB) is 1,024 kilobytes. A gigabyte (GB) is 1,024 megabytes. A terabyte (TB) is 1,024 gigabytes.

  • kb, Mb, Gb - A kilobit (kb) is 1,024 bits. A megabit (Mb) is 1,024 kilobits. A gigabit (Gb) is 1,024 megabits. A terabit (Tb) is 1,024 gigabits.

Don't forget! There are eight bits in a byte, so to translate from one to the other, you can multiply or divide by eight. For example, if you want to transfer 38MB across a 38 Mbps connection, it will take eight seconds.

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