Website Carbon Calculator
Every byte transferred uses energy in networks, data centers and devices. The calculator takes the page weight measured by Lighthouse and applies the Sustainable Web Design model (v3) to estimate grams of CO₂ per visit.
Results open in the site's full report, which you can share, compare and re-run.
What it checks
- Measured transfer size of the mobile homepage
- Number of network requests
- Estimated grams of CO₂ per visit (SWD model v3, global grid average)
- Performance metrics that usually improve when weight drops
Frequently asked questions
- How exact is the estimate?
- It is a model, not a measurement. It uses global averages for energy per gigabyte and grid carbon intensity, and it does not know your host's energy source.
- What makes pages heavy?
- Uncompressed images, video autoplay, large JavaScript bundles and third-party tags. The report's findings point to the biggest wins.
- Is a lighter page also faster?
- Usually. Less data means faster downloads, especially on mobile networks, which also helps Core Web Vitals.
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