Green Hosting and Page Carbon: Your Site’s Footprint
Every page view uses electricity: in the data centre that serves it, in the networks that carry it and in the visitor’s device. How much carbon that releases depends on two things you can influence: how much data the page transfers, and how the energy behind your hosting is produced.
Green hosting
The Green Web Foundation is a non-profit that keeps a public dataset of hosting providers that have shown evidence of running on, or offsetting their use with, renewable energy. Its greencheck service answers one question for a domain: is it served from one of those providers?
A provider gets listed by submitting evidence to The Green Web Foundation, such as its own renewable generation, renewable power contracts or energy certificates, which the foundation reviews. The listing is about the provider’s claims and evidence, not a measurement of your individual server.
“Not verified” doesn’t mean a host is dirty. Many hosts with renewable power have simply never applied, and the check can only recognise the network your site is served from. Behind a CDN, that’s the CDN.
How to improve it
- Ask your host whether it uses renewable energy and, if so, whether it is registered with The Green Web Foundation.
- When choosing a host or CDN, check it in The Green Web Foundation’s directory first.
- If you use a CDN, its listing is the one that counts for this check, so check the CDN too.
Carbon per page view
We estimate the CO₂ of one page view with the Sustainable Web Design model, using The Green Web Foundation’s open-source library CO2.js. The model turns the amount of data transferred into energy used by data centres, networks and devices, then into CO₂ using an average grid carbon intensity.
Treat the number as an estimate for comparison, not a measurement:
- It uses the global average grid intensity, not the grid where your server or visitors are.
- It assumes a first visit with nothing cached; returning visitors usually download much less.
- It doesn’t account for green hosting.
- The page weight comes from one mobile test load, so it changes with ads, consent banners and personalised content.
It is most useful for tracking your own site over time, and for seeing that a lighter page is a lower-carbon page.
How to reduce it
The biggest lever is transferring less data, which also makes the page faster:
- Images: serve modern formats (WebP, AVIF), size them for the layout and lazy-load images below the fold. See Image delivery.
- JavaScript: remove unused libraries, plugins and third-party tags. See JavaScript cost.
- Fonts: use fewer weights and subset them. See Web fonts.
- Video: don’t autoplay; load the player when the visitor asks for it.
- Caching and compression: long cache lifetimes for static files and Brotli or gzip compression mean repeat visits transfer much less. See Browser caching.
Page weight explains how to find what makes your page heavy.
How PerfoMetrix checks this
Green hosting. We send only the domain name to The Green Web Foundation’s public greencheck API. A verified green host passes and shows the provider’s name. Any other answer is information only and doesn’t lower the score. If the service can’t be reached, the check is shown as “couldn’t test”.
Carbon per page view. We pass the total page weight measured by the Lighthouse mobile test, which we already run for the performance section, to CO2.js with the Sustainable Web Design model (version 4). No extra requests are made to your site. The result is shown in grams of CO₂ per view and is information only: it is never scored.