Estimate carbon emissions of websites based on data transfer

Methodologies

• Sustainable Web Design (SWD) model (as of the end of 2023 the mainly used model by calculators)
• Time & location based approach (proposed by Fershad Irani)

See also CO2.js: Carbon estimation models

⚠ Accuracy of website carbon calculators

David Mytton:

Website carbon calculators are not very accurate, especially if they only use data transfer as the metric. Average values can’t represent the variety of applications which means they can’t be used for comparisons.

Many calculators make basic errors, taking figures from old academic papers or reports based on papers which are outdated or have suspicious methodologies. Always check how the calculations are performed and the sources for the energy intensity figure – has it been correctly adjusted for time? Do they caveat the calculations with anything mentioned above?

— Approaches to calculating website energy and carbon by David Mytton

Fershad Irani:

So, is data transfer a good proxy?
No, data transfer probably isn’t the best proxy from website carbon emissions. Right now, though, it’s the best we’ve got given the tools and knowledge available to us.

— Is data transfer the best proxy for website carbon emissions? - Fershad Irani

DebugBear:

Website CO2 calculators measure page weight and assume emissions grow proportionally with page weight. However, page weight is not a useful predictor of the greenhouse gas emissions generated by a website.
[…]
Again, page weight is a terrible proxy for energy consumption. The user might load a 10 megabyte image, but this static file requires little server-side processing. At the same time, loading a 10 kilobyte HTML document might require lots of processing to generate.
[…]
A large static site would get a poor rating from website carbon calculators, despite using little energy on the server. But a small page built using many complex database queries will incorrectly get a good rating.

Tools

Green Web Check

Tool from the Green Web Foundation to check if a website is hosted by a green provider that uses data centers powered by renewable energy.

URL: https://www.thegreenwebfoundation.org

Website Carbon Calculator

Tool created by Wholegrain Digital that estimates the carbon impact of a webpage.

URL: https://www.websitecarbon.com

Ecograder

Tool created by Mightybytes to calculate a score (1-100) and to estimate the carbon emissions based on page weight and performance. It uses the CO2.js library and the Google Lighthouse's page metrics for the calculation.
It provides many tips on how to improve the user experience and how to reduce the page size.

URL: https://ecograder.com
Methodology: CO2.js Case Study - Ecograder by Mightybytes

Digital Beacon

Calculates the CO2 emissions and page size and gives some useful tips for improvement.
It calculates the impact based on data transmission which can be accurately measured and by using two numbers that represent kWh per GB and CO2 per kWh.

URL: https://digitalbeacon.co

EcoPing

Calculates the website carbon emissions based on the information from Sustainable Web Design, but with actual live grid intensity data and energy emissions based on location (not hosting provider).
One site is for free, more does cost (→pricing).
Useful to track website emissions over time.

URL: https://ecoping.earth

GreenFrame.io

greenpixie

URL: https://greenpixie.com/website-carbon-calculator

Methodology:

• calculation based on data transmission
• uses Energy Carbon Intensity factors from the National Grid

Statsy

URL: https://statsy.com/docs/carbon/emission-calculator

Statsy is the easy way to measure your website traffic, performance, and carbon footprint.

How it works:

Rather than relying on transfer size and monthly visits, we collect all requests from the website and store them as logs in our database. This allows us to account for dynamic elements, lazy loading, client-side routers, and personalized content, providing a more accurate estimate of your website's carbon footprint.

Klimatest (°Cleaner Web)

URL: https://klimatest.cleaner-web.com

Findet heraus, wie nachhaltig eine Website ist, wie viel CO₂ sie ausstößt und in welchen Bereichen Nachholbedarf besteht. Der Test ist eine erste Annäherung - er ist nicht vergleichbar mit einem umfassenden Audit.

Comparison to other calculators:

Der Website-Klimatest kann noch mehr, detailliertere und exaktere Informationen ausgeben. Außerdem bietet er individuelle Verbesserungstipps an.
Was ihn in seiner Analyse unschlagbar macht, ist das ausgeklügelte Bewertungssystem, das eine Website auf 34 Faktoren hin überprüft. Hier sind Werte abgedeckt, die den kompletten Prozess des Website-Betriebs einbinden, von der Datenlagerung auf dem Server über die Übertragung der Daten bis zur Benutzung der Website auf dem Endgerät.
Zudem bezieht sich der Website-Klimatest auf die spezifischen Stromnetze der DACH-Region (Deutschland, Österreich, Schweiz) und auf lokale Grid Intensities im Stromnetz – und liefert dadurch sehr präzise Ergebnisse.
— Den Carbon Footprint einer Website herausfinden

ecoIndex

URL: https://www.ecoindex.fr/en/

Uses three criteria in its calculation algorithm:

• DOM complexity (highest priority, 3x)
• HTTP requests (medium priority, 2x)
• data transferred size (low priority, 1x)