Upload and download speeds explained

Friday, 9 March, 2018

When broadband companies try to attract new customers they talk a great deal about line speed.

Specifically, they’re referring to how quickly information can be downloaded from a host web server to your home or office.

Marketing literature rarely acknowledges there are actually two metrics used to measure internet speeds – upload and download speeds.

Download speeds steal all the headlines, but upload speeds are also important if you want a dependable internet service.

We define upload and download speeds below and explain how to measure them. You can test your upload and download speed here to see how you measure up!

What is bandwidth?

You can think of a broadband connection like a road, where data flows from a point of origin to a destination at the fastest speed that particular line allows.

Some lines are able to support higher volumes of traffic (like dual carriageways) or transmit data really quickly (motorways).

However, other lines are the digital equivalent of single carriageways, where congestion slows everything down.

When broadband providers talk about line speed, they generally mean the maximum speed limit that particular connection is capable of, not the speed you’ll actually achieve.

The latter depends on various factors:

  • The quality of underground cables installed by Openreach or Virgin (who use their own network)
  • The physical distance between your home/office and the nearest green Openreach pavement cabinet (Virgin is more binary – it’s either there or it isn’t)
  • The quality and reliability of your own equipment

Sometimes, your broadband router or micro filters put a limit on connection speeds. On a 70mph motorway, a lorry limited to 56mph will never achieve the maximum speed.

Also, maximum speeds are measured to the first piece of hardware in your home – usually a broadband router.

Since WiFi is quite inefficient, the actual speed of data arriving onto laptops and tablets will be well below the speed recorded at the router or hub.

How is data measured?

Broadband providers talk about Mbps as a measure of connection speeds, but this is a meaningless number without understanding the process involved.

Data is transmitted via individual packets called bits.

These contain all the information required to view web pages, stream TV programmes, send and receive emails, etc.

A million bits make up a megabit – the Mb figure quoted in line speed calculations.

This shouldn’t be confused with megabytes – the physical size of a digital file, written as MB.

There are eight bits in every byte, so a line speed of 20Mbps (Megabits per second) could theoretically transmit 2.5MegaBytes of data per second.


We tend to passively consume internet content – looking at social media, watching video content, reading blogs, etc.

Every time we access a webpage or view a file, its contents have to be downloaded to our devices.

Sometimes every packet has delivered before we can access it (opening a PDF), whereas at other times, the packets arrive in a continuous stream (watching Netflix).

These are all examples of downloading.

When broadband providers talk about speeds, they mean download speeds – we’re consumers far more than we’re content generators.

But what if we want to submit something to the internet?


Uploading information is very different – the return journey in the motorway analogy given above.

When we upload data, we’re asking our broadband routers and landlines to send information back to other people.

Internet service providers have prioritised downloads, since that’s what consumers need an internet connection for most of the time.

Upload speeds are usually much slower than download speeds – like a motorway with roadworks on one side but not the other.

As a result, it’s much quicker to receive a 1MB email than it is to send one.

That’s a problem for any two-way communications, like online gaming or video chats.

A decent upload speed is very important for people who want to communicate via Skype, Xbox Live, email, etc.

How can I check my upload and download speeds?

Broadband providers often ask you to check line speeds if you report a technical fault.

All you have to do is visit a website with the ability to measure connection speeds, and dedicated software will perform line speed checks for you.

The results are displayed in Mbps and the download speed will be much higher than the upload speed.

This gives you an accurate, live summary of how your internet connection is performing.

The best free checker is located at BroadbandDeals Speed Test.

Simply click “start speed test”, and you’ll be given two boxes showing you your current Download Speed and Upload Speed. You can do this test for free as many times as you like.

MAIN IMAGE: k_e_lewis/CC BY 2.0

Neil Cumins author picture


Neil is our resident tech expert. He's written guides on loads of broadband head-scratchers and is determined to solve all your technology problems!