How our website carbon calculator works
Our free website carbon calculator is a powerful tool for understanding your digital sustainability performance. To support your organisation's transformation, it turns website data into measurable business results that you can take and run or use to power up your website.
Our tool uses the Green Web Foundation's trusted CO2.js open-source library and advanced performance metrics. This means you get a full digital sustainability score (not just your website's carbon footprint) but also the performance and hosting factors that impact it!
How our website carbon calculator compares
Not all carbon calculators are the same. Many tools stop at basic page weight and data transfer estimates. Here's what makes ours slightly different.
The technical details
What powers the carbon calculator and why
At the heart of our website's carbon calculator is the @tgwf/co2 library from The Green Web Foundation. This is a great base to start from. The framework is based on energy intensity research, network energy models, device power consumption and international Energy Agency data. Plus, the library is maintained with regular updates, as documented in their GitHub repository and release notes.
How our carbon calculator measures more than just carbon
The tech behind the advanced measurements
Performance metrics
We integrate Google PageSpeed Insights API data because performance directly affects energy consumption:
• Core Web Vitals: Loading speed impacts server processing time and energy use
• Resource optimisation scores: Inefficient code wastes computational power
• Caching effectiveness: Poor caching multiplies energy consumption
• JavaScript execution time: Long-running scripts drain device batteries
Green hosting verification
Our tools for measuring website carbon footprint verify renewable energy usage through:
• Real-time Green Web Foundation API checks
• Hosting provider renewable energy certifications
• Data centre location and regional energy mix
• Carbon offset program participation
Resource efficiency analysis
Beyond basic file sizes, we measure:
• Compression effectiveness: How well your content is optimised
• Unused code detection: Resources loaded but never used
• Image optimisation levels: Oversized images waste energy
• Third-party script impact: External resources affecting sustainability
How it works out your grade
Page load times:
• Browser automation loads your page like a real visitor
• Every HTTP request is tracked and categorised
• Actual transferred bytes are measured (including compression)
• Multiple page loads ensure accuracy
Performance calculation:
We measure website carbon emissions alongside:
• Load time impact on energy use
• Resource efficiency scores
• User experience metrics
• Optimisation opportunities
Your final digital sustainability assessment combines:
• Raw carbon emissions (g CO₂)
• Performance efficiency rating
• Green hosting bonus
• Overall sustainability grade
Understanding your calculator results
Carbon emissions breakdown
• Per page view: Your website carbon per visitor
• Annual projection: Based on typical traffic (365,000 visits/year)
• Comparison: How you stack up against the 0.5g CO₂ average
• Real-world equivalents: Smartphone charges, LED hours, trees neededPerformance impact on sustainability
See how performance affects your digital carbon footprint:
• Slow load times = higher energy consumption
• Inefficient code = wasted processing power
• Poor caching = repeated energy use
• Large DOM = increased device strainImprovement recommendations
Our AI-powered insights (using OpenAI GPT-4.1-nano) analyse your complete profile to suggest:
• Quick wins for immediate carbon reduction
• Performance fixes that lower emissions
• Long-term sustainability strategies
• Specific technical optimisations
Learn more about digital sustainability
Discover why sustainable websites eliminate team friction and boost the bottom line. Free cross-team checklist inside! 🙌
Wanna give it a whirl?
Try the Website Carbon Calculator to uncover where to cut carbon, save money, and streamline performance. ❤️🌍
As this calculator is in beta, we are continuously working to improve its accuracy and usefulness, with the ultimate aim of providing a truly helpful and transparent tool for understanding website sustainability. This thorough approach, even in its development phase, strives to provide a realistic baseline of your site's performance and environmental impact, forming the foundation for informed, actionable insights. (Suggested link: Learn more about our methodology and beta phase)