How the Index is measured
I built The Green Blind Spot to answer one question: how much CO2 does a company's website emit per visit? Brands that make public sustainability claims often don't see the footprint of their own websites; this index measures it. Here is exactly how I get that number, and where it falls short.
A starting point
I built this index to start a conversation. The model is not perfect, and it will get better. Each time I change it, I will publish what changed, what I got wrong and what held up, so everyone can learn from it.
I am not an expert on ecological footprints. I am an SEO, and I kept running into this in my work with clients: many brands don't realise their website has a footprint at all.
What I measure
Each company's 30 most-visited pages, based on estimated monthly search traffic from DataForSEO. I open each page in a real Chromium browser at a normal desktop screen size, and scroll down it five times so that content which only loads as you scroll (images, ads, embedded widgets) gets counted too. Then I add up every byte the page transferred.
From that byte count I get:
- CO2 per page view: one page's transferred bytes converted to grams of CO2 with the Sustainable Web Design Model version 4 (the same model websitecarbon.com uses): 0.30 kWh per GB transferred across data centres, networks and devices, at the global average 494 g CO2 per kWh, about 0.148 g of CO2 per MB.
- CO2 per visit: this is the number the ranking is sorted by, and it is not just one page's figure. I take the CO2 per view of every page I measured for that company and average them, weighting each page by how many of the company's visits actually go to it. A page almost nobody visits barely moves this number, even if it happens to be heavy; a page that gets most of the company's traffic moves it a lot. This is meant to reflect what a typical visit to the company's site actually costs, not the worst or best single page.
- Annual CO2 for a page: that page's CO2 per view multiplied by its estimated monthly visits, multiplied by 12.
- Annual CO2 for a company: the sum of that figure across all the pages I measured for it. I estimate this internally, but the ranking published here sorts by CO2 per visit, not by annual footprint.
- Traffic coverage: what share of the company's total estimated visits the pages I measured actually account for. I publish this next to every company's number so you can see how representative it is.
Fewer than 10 pages, no number. If I could only measure fewer than 10 pages for a company, or its estimated traffic is under 100 visits a month, I don't publish a number for it. It stays out of the ranking rather than being shown with a number I don't trust.
How I rank companies
Lightest first, by CO2 per visit (rank 1 is the lightest site). This treats a small brand and a global one the same way, because it doesn't matter how popular the site is, only how much it costs the planet each time someone loads it.
Why I show a letter grade and a peer band, not just one number
Every company also gets a letter grade, A+ through F, using the Sustainable Web Design Model's own rating scale (A+ is up to 0.040 g per visit, F is anything above 0.359 g). In this edition, measured 2026-10-02, the median company here emitted 1.78 g per visit, about 5.0× the cutoff for the lowest passing grade, so almost everyone gets an F. That is a real finding about how heavy sustainability-branded websites tend to be.
I don't adjust this scale to flatter the companies in this Index. Inventing a softer scale just for this group would be the first thing a company could point to if it disputed its result.
Because almost everyone fails the letter grade, I also show a peer band: where a company sits against the others in this same edition, from lightest 25% up to heaviest 25%. I calculate this after removing companies I couldn't measure fairly, and I recalculate it every edition, so a company's peer band can shift because the companies around it changed, not only because its own site changed.
How the letter grades are set
Every grade is a fixed cutoff in grams of CO2 per visit, from the Sustainable Web Design Model version 4 rating scale. I don't move these to make the results look better or worse.
The cutoffs come from page weights in the HTTP Archive, a public record of how millions of web pages are built. A+ is the lightest 5% of web pages. The line between E and F is the median web page, about 2.4 MB.
| Grade | CO2 per visit |
|---|---|
| A+ | up to 0.040 g |
| A | up to 0.079 g |
| B | up to 0.145 g |
| C | up to 0.209 g |
| D | up to 0.278 g |
| E | up to 0.359 g |
| F | above 0.359 g |
Who is included
Companies that publicly position themselves on sustainability: certified B Corps, companies with a public net-zero or science-based target, consumer brands that market themselves as sustainable, or companies whose core product is a climate or environmental technology. I curate and version this list myself, and a company's inclusion is based on its own public claims, never on whether it is a client of mine.
Anyone can suggest a company, including their own. I review each one against these criteria and decide. Submit a site for review.
How the comparisons are worked out
The Is that a lot? page and the short lines on company pages translate grams and tonnes into everyday terms. Grams become electricity with the model's own figure, so those comparisons add no second carbon number; the car comparison converts CO2 to CO2. These are the only outside numbers:
- Electricity behind each gram of CO2: 494 g CO2 per kWh. Sustainable Web Design Model v4, the model every number on this site uses.
- LED bulb: 10 watts. A chosen everyday reference: a common household LED bulb.
- A Dutch home's electricity: 2,430 kWh a year. Milieu Centraal, based on CBS data 2010 to 2024 (homes heated with gas or block heating).
- Average new car sold in Europe in 2025: 96.7 g CO2 per km. European Environment Agency, provisional data, 25 June 2026. This is the official test figure; real driving emits more, so the real distance would be shorter.
- The Earth's circumference: 40,075 km. At the equator; used only for the "around the Earth" comparison.
One visit: grams ÷ 494 g per kWh = kWh, then minutes of a 10-watt bulb. One year: grams ÷ 96.7 g per km = car kilometres; grams ÷ 494 g per kWh ÷ 2,430 kWh = Dutch homes; car kilometres ÷ 40,075 km = trips around the Earth. Yearly figures cover estimated search visits to the pages measured only, so they understate the real total.
What this does not capture (read this before citing a number)
- Only estimated organic search traffic counts. Visits from direct links, paid ads, social media and other sites referring people in are not included, so the total annual CO2 figures understate the real total. This applies evenly across every company, so comparisons between companies still hold.
- Only the top 30 pages, not the whole site. I publish the traffic coverage percentage for each company so you can judge how complete that picture is.
- No adjustment for green hosting yet. The model lets a site on renewable-powered servers remove the data-centre share of its figure, which would make it at most about 18% lower. The 2026 editions leave it out, so they can be compared with each other. I plan to add it from the January 2027 edition and will say on this page what changed. websitecarbon.com already applies it, so a green-hosted site can score a little lower there than here.
- Pages here come out heavier than a basic load. I scroll each page to load lazy content, while the HTTP Archive behind the grade scale measures pages without scrolling.
- No allowance for browser caching. Every visit is measured as if it were a first-time visit, not a returning one where the browser already has some files stored.
- Measured against United States, English-language search by default. Some companies have a different market set in my configuration, but for any company without one, and whose real audience is mostly outside the US, its traffic and total footprint will be understated. Again, this is applied consistently, so relative ranking is still meaningful.
- Not the same numbers as my client reports. For client work I run a separate tool calibrated to match Screaming Frog, which uses an older conversion. The Index does not use it.
- These are estimates, produced the same way for every company. The Index is built to compare companies against each other fairly, not to state the exact carbon cost of a single visit to any one of them.
How often this runs
Monthly measurement, quarterly ranking. I re-measure every company's website monthly, and publish a new headline ranking every quarter. Companies I couldn't measure fairly are re-checked at every monthly crawl.
If something looks wrong
Tell me and I'll re-measure. Use the dispute form on that company's page, or email letsgrow+greencrawl@baba-seo.com. Tell me what looks off and I'll re-measure and reply.