# Carbon Tracking
TIP
Carbon tracking requires a PRO account.
# How it works
Carbon tracking works by analysing all the files loaded on your website to calculate the total bytes loaded. Your page is only analysed if:
- It receives page views.
- It has been longer than 3 days since the last analysis.
- It has been modified. We know this by checking the page header last-modified and comparing the html against our last saved hash. This way we can save energy by skipping unnecessary assets if they haven't changed.
Each analysis run is stored as a historic log for that page.
# How much a visitor loads
Once we have a total bytes for your page we determine how much a visitor might have loaded by assigning them a percentage.
- Their first visit - 100%
- Their first visit to the page, but not to your domain - 50%
- Not their first visit to the page - 5%
# How CO2 is calculated
We've updated our CO2 calculations (25/08/2022) to utilise The Green Web Foundation's CO2 (opens new window) library. This has been enabled by the work explained in Sustainable Web Design - Calculating Digital Emissions (opens new window), which is regularly updated to include the most recent research and information.
Our old method was explained in a previous post here (opens new window).
We check your website against The Green Web Foundation API to determine if you are using a green host.