A website with 10,000 monthly page views producing 4.61g CO2 per visit generates approximately 553 kg of CO2 per year — equivalent to driving a car 2,200 km. By optimizing your website, you can reduce this by 50-80%, while simultaneously improving user experience and search engine rankings.
How it works?
Understand our science-based approach to measuring and certifying your website's environmental impact.
Four Steps to Certification
1
Scan & Measure
Enter your website URL and we run a comprehensive analysis. We measure the total data transfer of your page, test loading performance via Google PageSpeed Insights (measuring Core Web Vitals, accessibility, SEO and best practices), and assess hosting infrastructure. All measurements follow the Sustainable Web Design (SWD) v4 model.
2
Carbon Calculation
Using the measured data, we calculate your website's carbon footprint in grams of CO2 per page view. The calculation accounts for the energy consumed across four system segments: data centers, networks, end-user devices, and the production of hardware. We factor in your hosting country's carbon intensity of electricity to provide location-specific results.
3
Score & Certify
We generate a composite score from 0 to 100 based on your carbon footprint, PageSpeed performance, accessibility, SEO, and best practices. Websites that score above our thresholds receive a star-rated EpicStamp certificate (1 to 3 stars) proving their commitment to sustainability.
4
Monitor & Improve
Choose a 1, 2, or 3-year subscription for ongoing monitoring. Your website is re-scanned monthly to ensure it maintains its eco-friendly status. You receive regular reports, actionable recommendations for improvement, and a dashboard to track your progress over time.
Our Methodology: Sustainable Web Design (SWD) v4
We use the industry-standard SWD model version 4, developed by the Green Web Foundation, to calculate the carbon emissions of websites.
What is the SWD Model?
The Sustainable Web Design (SWD) model is a peer-reviewed, open-source methodology for estimating the carbon emissions associated with digital products and services. Version 4 of the model was developed collaboratively by the Green Web Foundation, Wholegrain Digital, Mightybytes, and Medina Works.
The model translates data transfer (in bytes) into energy consumption (in kWh), and then into carbon emissions (in grams of CO2e), by accounting for the entire system that makes the internet work.
The Four System Segments
The SWD v4 model divides internet infrastructure into four segments, each with its own operational energy intensity (kWh per GB of data transferred):
Data Centers
0.055 kWh/GB
The servers that host websites and process requests. This includes server compute, storage, cooling, and facility overhead.
Networks
0.059 kWh/GB
The telecommunications infrastructure that transmits data between servers and users, including routers, switches, and undersea cables.
User Devices
0.080 kWh/GB
The laptops, phones, and tablets that visitors use to access your website. This covers the energy consumed during data processing and display.
Hardware Production
0.081 kWh/GB
The embodied energy in manufacturing the hardware used across all three operational segments (servers, network equipment, and user devices).
Total Energy per Visit
Energy (kWh) = Data Transfer (GB) × (0.055 + 0.059 + 0.080 + 0.081)
That's a combined 0.275 kWh per GB of data transferred. This is then multiplied by the number of monthly visitors and the carbon intensity of the hosting country's electricity grid.
From Energy to Carbon
Once we know the energy consumption, we convert it to carbon emissions using the carbon intensity of the electricity grid where the website is hosted. Carbon intensity varies significantly by country:
🇫🇷
France: ~56 gCO2/kWh
(mostly nuclear)
🇩🇪
Germany: ~385 gCO2/kWh
(mixed energy sources)
🇺🇸
USA: ~379 gCO2/kWh
(varies by state)
🇳🇴
Norway: ~29 gCO2/kWh
(mostly hydroelectric)
Carbon Emissions Formula
CO2 (grams) = Energy (kWh) × Carbon Intensity (gCO2/kWh)
A website hosted in France on a nuclear-powered grid produces roughly 7x less CO2 than the same website hosted on a coal-heavy grid.
Returning vs. New Visitors
The SWD v4 model accounts for browser caching. Returning visitors typically load fewer resources because their browser has cached static assets (images, CSS, JavaScript) from previous visits.
We apply a 2% caching factor for returning visitors, meaning they transfer only about 2% of the total page weight on subsequent visits. Combined with an estimated 75% first-time / 25% returning visitor ratio, this significantly affects the average carbon per visit.
Green Hosting Bonus
If your website is hosted on a verified green energy provider (checked via The Green Web Foundation's database), we apply a reduction factor to the data center segment. Green-hosted sites receive a lower carbon calculation, reflecting their use of renewable energy sources.
PageSpeed & Quality Scoring
Beyond carbon emissions, we evaluate your website using Google PageSpeed Insights, which measures four key areas:
90+
Performance
Core Web Vitals including Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Total Blocking Time (TBT).
90+
Accessibility
ARIA labels, color contrast, keyboard navigation, screen reader compatibility, and semantic HTML.
90+
Best Practices
HTTPS usage, image optimization, console errors, deprecated APIs, and modern browser standards.
90+
SEO
Meta tags, structured data, crawlability, mobile friendliness, and link quality.
Each PageSpeed category score contributes to your overall EpicStamp rating. Sites with better performance naturally transfer less data and consume less energy per visit.
Composite Score Calculation
Your final EpicStamp score (0-100) is calculated as a weighted average:
40%
Carbon Footprint Score
Based on CO2 per page view relative to the global average (0.5g baseline)
25%
Performance Score
Google PageSpeed performance audit
15%
Accessibility Score
Google PageSpeed accessibility audit
10%
Best Practices Score
Google PageSpeed best practices audit
10%
SEO Score
Google PageSpeed SEO audit
Star Rating System
Your certification level depends on how well your website meets sustainability requirements.
90%+ Score — Excellent
Your website is among the cleanest on the internet. Exceptional optimization, minimal carbon footprint, and outstanding technical quality.
80%+ Score — Good
Your website performs well above average. Strong sustainability credentials with room for minor improvements.
70%+ Score — Certified
Your website meets the baseline sustainability standard. A solid foundation to build upon with our recommendations.
Why It Matters
4.61g
Average CO2 per page view worldwide
2%
Of global CO2 emissions come from the internet (comparable to aviation)
10
Trees planted for every EpicStamp certificate purchased
Built on Open Standards
SWD v4 Model
Developed by the Green Web Foundation, Wholegrain Digital, Mightybytes, and Medina Works. Peer-reviewed and open source.
sustainablewebdesign.orgCO2.js Library
The Green Web Foundation's JavaScript library that implements the SWD model for calculating digital carbon emissions.
developers.thegreenwebfoundation.orgGoogle PageSpeed Insights
Industry-standard tool for measuring web performance, accessibility, best practices, and SEO.
pagespeed.web.devEmber Climate Data
Provides country-level carbon intensity data for electricity grids, updated annually.
ember-climate.orgReady to measure your website's impact?
Enter your website URL to get a free carbon footprint analysis.