What does Green Meter measure?

Green Meter measures the actual weight (in bytes) that each page of this site transfers to the visitor's browser, and translates that weight into an estimate of CO2 emissions per visit using a public and reproducible model. The measurement is not a simulation or a synthetic test: it is real data collected from real visits.

What is measured exactly

• Transferred size (including compression) of every resource downloaded by the browser: HTML, CSS, JavaScript, images, web fonts, embedded videos and third-party requests (analytics, maps, embeds).
• Weight of CSS and JavaScript files that WordPress enqueues on the server side, as a complement to the browser data.
• Hosting type (renewable or not) verified against the public database of The Green Web Foundation.

What is NOT measured (honest limitations)

• Browser cache: a second visit transfers far fewer bytes than the first, which can inflate or deflate the average depending on recurring traffic.
• The specific consumption of each visitor's device and network: the model applies aggregated averages per byte transferred (including the embodied emissions from hardware manufacturing), not individual measurements.
• Visitor's geographic location: the actual carbon intensity varies depending on each country's electrical grid. The SWD model applies a global average.
• Energy consumed by edge CDNs serving the content — the model's aggregate factor is assumed.

How to verify it yourself

Open your browser's DevTools (F12 or right-click → Inspect), go to the Network tab, reload the page and look at the "Transferred" total at the bottom. That value should match, within a reasonable margin, the weight Green Meter shows for this page.

How is it different from other tools?

Most web carbon footprint measurement tools — such as Website Carbon or Ecograder — analyze a URL from the outside, offering a static, one-time data point. Green Meter works differently:

• Real measurement from within
  — uses the browser's Performance API to capture the actual transferred size of each resource, not an external estimate.
• Per-page data
  — each page shows its own grade and CO2, not a generic domain-level figure. This lets you identify which specific pages need optimization.
• Continuous monitoring
  — measurements are automatically updated with each visit, reflecting the real state of the site at all times.
• Automatic green hosting detection
  — queries The Green Web Foundation API to verify whether the server uses renewable energy and adjusts the calculation accordingly.

Methodology and data sources

CO2 calculation: Sustainable Web Design Model v4

Emissions are calculated with the Sustainable Web Design (SWD) model v4, maintained by Wholegrain Digital and The Green Web Foundation. It estimates 0.145 grams of CO2 per megabyte transferred: 0.300 kWh per GB (operational energy plus embodied emissions of data centers, transmission networks and user devices) multiplied by the average carbon intensity of the world electricity grid (494 g/kWh, data from Ember). Full documentation at sustainablewebdesign.org.

Formula used

CO2 (g) = bytes transferred / 1,048,576 × 0.145 g/MB × green hosting adjustment (× 0.817 if verified renewable hosting: data center operational emissions are zeroed out).

The model factor is modifiable from code via the wlc_gm_co2_factor filter, which allows the calculation to be aligned with future SWD revisions without touching the database.

Grading system

Grades from A+ to F follow the official Digital Carbon Ratings, recalibrated for the SWD v4 model from HTTP Archive percentiles: A+ corresponds to the 5% most efficient pages in the world, E to the global average and F to anything above it.

Green hosting

If the hosting provider uses renewable energy, as verified by The Green Web Foundation, data center operational emissions are zeroed out following the SWD v4 model — a reduction of roughly 18% of the calculated total.

Dual measurement system

Server-side: on each render the plugin measures the weight of the CSS, JS and HTML files that WordPress enqueues. Client-side: it runs a lightweight script in the browser that reads the Performance API del navegador and reports the size actually transferred for each resource (compression included). The browser data takes precedence when available because it reflects observable reality; the server-side data is the fallback.

Frequency and sampling

Every real visit to the site adds a measurement to the table. Per-page averages are calculated over the latest stored measurements (rolling window). There is no sampling or filtering: all visits are processed except those to the WordPress backend and to the /green-meter page itself (to avoid contaminating the data).

Measured pages