The world’s first carbon calculator for websites

Written by Tom Greenwood - May 22, 2018

Our mission has always been to not just create a sustainable business, but to use our business to help drive progress towards a more sustainable future. We work hard to minimise the environmental impact of our day to day operations and we’ve always designed our products and services to be largely immaterial, leading to us being a digital agency.

However, we’ve become increasingly aware that the digital world that we work in is not as clean as it appears. If you take the internet as a whole, it has roughly the same emissions as global aviation, but it’s growing much faster and could reach 3.5% of global greenhouse gas emissions within 10 years. This results from the huge amount of electricity required to process and transmit the data that we send around the globe. Despite our good intentions, it seems that we now work in one of the world’s most polluting industries.

So what are we doing about it?

It’s essential that we as a team take leadership on this issue and help our clients to reduce the environmental impact of their websites.  Some things:

  1. Educate ourselves and share knowledge
  2. Set goals
  3. Improve energy efficiency
  4. Use greener energy sources
  5. Measure and improve

One big thing that has been missing from our process is a way to calculate the carbon emissions of a website. It was famously said by Peter Drucker that “you can’t manage what you can’t measure”, and so it is essential that we have a way to measure website efficiency and carbon emissions. Yes, there are lots of excellent performance optimisation tools on the market, but none of them can tell us the energy consumption or emissions. It’s all very well knowing that the internet is 2% of global emissions, but how does that relate to an individual website or web page?

We need to know, and so we set about developing a method to work it out a couple of years ago. We’ve had a prototype in a spreadsheet for about a year, but are pleased to be able to share an early iteration of this with the wider web community now at

You can go there right now and test the home page of any website to find out the CO2 per page view, and if you know the traffic volumes, you can also see the annual CO2 emissions and energy consumption alongside illustrations to help put the numbers into perspective.

How does it work?

Finding a way to calculate energy and emissions for a website without doing a full lifecycle assessment has been a real challenge. Our goal has been to create a tool that anyone can use quickly and easily, ideally for little or no cost. The key to achieving this has been in identifying that there’s a correlation between data transfer and energy consumption, as well as between energy consumption and emissions. By combining existing research with some of our own data, we’ve been able to develop a system that can calculate the emissions of a web page and the approximate energy used for each page load by the data center, telecommunication network and end user device.

You can read more about it here, and we hope to publish more in depth information when we get time.

What has it revealed so far?

We’ve found that there’s a huge spectrum of efficiency. We compare sites using CO2 per page view so that traffic volumes are taken out of the equation and websites can be compared on a level playing field.

So far the most efficient website tested is, which is the brutally bare bones website for Elon and Kimbal Musks non-profit foundation. It comes comes in at 0.009 grams of CO2 per page view.

The least efficient website tested to date is with a staggering 21.57 grams of CO2 per page view. Imagine how that must have added up recently with traffic interested in Meghan and Harry’s wedding! That is probably more than the weight of their wedding rings produced in emissions, every time someone visits the site.

The official website of the UK Royal Family is highly inefficient

We’ve used the design and development of as a learning exercise and challenge within our team to see how far we can push the emissions down without compromising user experience. Key strategies that we’ve used include the use of native fonts, SVG icons, and the avoidance of photos, videos and unnecessary scrips. This has allowed us to achieve a current efficiency of 0.083 grams of CO2 per page view.

How accurate is it?

In the absence of a detailed lifecycle assessment, all carbon calculator tools are actually carbon estimators. Measuring the CO2 produced by a website precisely would be near (if not actually) impossible, so assumptions need to be made in order to make it practical.

We’ve had to make a number of assumptions about the website, user behaviour, devices, infrastructure, and power supply. There will always be exceptions to the rule, but the aim is to represent a typical scenario with a reasonable degree of accuracy. This allows us to not only get useful figures for each website, but to compare different websites through a standardised methodology, and therefore benchmark websites against each other to drive continuous improvement.

We’ll continue to do our own research and examine new data to keep improving the accuracy of the results and to take more factors into account, but even in this first version we believe that we’ve achieved a sufficient level of accuracy to make it meaningful and effective in helping our industry to lower emissions.

What’s next?

In addition to continuously improving the accuracy of the tool, we will gradually roll out more features and publish content to help people learn about the causes of website emissions as well as the practical steps that can be taken to reduce them. We’ll also be sharing interesting data that we gather moving forward and are already embedding efficiency and carbon reduction into our core design and development processes with our clients. We also have plans on our roadmap for the development of other tools that build upon the carbon calculator and offer more advanced monitoring on a range of metrics.

This is simply one early step in a very exciting journey.