Fooled By Website Carbon Calculators

„Fooled by the Website Carbon Calculator“ – Roberta Haseleu

Website Carbon Calculators are good for awareness about energy consumption of the IT sector, but they currently work based on very rough estimations. Therefore more transparency is needed as well as better tools for developers to create better, more energy efficient code – this is the current conclusion by Roberta Haseleu.

She gave a 15 minute talk at Chaos Communication Camp 2023 about her tests with the existing carbon calculator tools, I recommend it very much:

Talk: „Fooled by the Website Carbon Calculator. Green Coding & Measuring the Environmental Impacts of IT“ by Roberta Haseleu, Chaos Communication Camp 2023

Website Carbon Calculators mentioned in her talk:,,, She also mentioned the startup, which helped with the test cases. The stage was hosted by Bits & Bäume.

Personally I’m very thankful for this talk and somebody doing some real testing.

Web Sustainability Consultant Fershad Irani also published insightful articles in the past months in regards to the challenge of measuring CO2 of websites:

He referred in particular to this talk „The Internet of tomorrow must sleep more and grow old“ by Romain Jacob und Laurent Vanbever, in which I personally learned a lot more about the energy challenge in IT and in regards to server infrastructure.

For an full picture of the current state of the internet and fossil fuel consumption, I can’t recommend this talk enough:

I really hope this conversation will continue!


Green Coding Berlin commented on LinkedIn:

I have also seen the talk by Roberta and I have to say that I was a bit suprised about her suprise (pun intended) that the values differ and that only network transfer is looked at.

The calculators typically state quite clearly what they are doing and why. The arguably most popular one has a „How does it work“ in the first line of the page. Others are similar.

I felt it shined a unnecessary bad light on what these tools are doing.

Having said that: It is possible though to look at the full stack if you use something like the Green Metrics Tool you mentioned (which we are developing.).

Here are some projects we are monitoring:

Here an example for a WordPress sample with database, webserver and browser:

2. If you want to have a better overview over the differences of Website Calculators in particular I can recommend this great article from marmelab :

LinkedIn comment by Green Coding Berlin

More resources

A place for following the discussions is the „#greener-webdev“ channel at Climate Action Tech Slack:

Feel free to join, there are local channels like local-germany, local-austria, local-switzerland, etc. etc.

On my blog I also published two articles about Green Web & Energy Consumption in german:

Article images: Screenshots of talk by Roberta Haseleu,


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