Digital emissions
How we measure the site’s carbon emissions
For our site’s homepage, we estimate emissions at 0.06g of CO2-equivalent per page view as of July 2025. This corresponds to a rating of “A” on the Digital Carbon Ratings scale, in the top 10% of sites by page weight.
We review the site’s emissions with the Sustainable Web Design (SWD) methodology, version 4. It’s an established way to calculate the carbon footprint of content websites, and individual web pages, based on the weight of the pages and how much traffic they receive.
Here are the underlying factors we use to calculate emissions:
- We measure the page weight at 492 kb for first-time visitors and 41.9 kb for return visits. This is measured with Google Lighthouse (via DebugBear) set up for Mobile emulation.
- We use a grid carbon factor of 484.4 gCO2e/kWh for network and user devices operational emissions. This is the "World" figure of country-level carbon factor data from Ember.
- We use a grid carbon factor of 317.9 gCO2e/kWh for operational data center emissions (Ireland).
Why we use this methodology
We use a wide range of digital emissions methodologies depending on the needs of the project. For wagtail.org, we chose:
- SWD to make figures more comparable with common emissions calculators.
- Google Lighthouse, as its assessment of page weight on first page load is well established.
- Simulated Mobile testing, rather than desktop as web traffic worldwide is trending towards majority on mobile devices.
- The homepage, as it’s the most-viewed page of the site (50% of visits).
- A static “one-off” measurement, to avoid adding a badge that would necessarily use up more resources to load.
Monitoring emissions over time
We use DebugBear to check representative pages of the site for performance and other content health considerations on a weekly basis. There are alerts in place to make sure page weight (and emissions) stay within our target.