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Carbon Calculation Methodology

Overview

This document provides a comprehensive explanation of how our website carbon calculator derives carbon footprint estimates. Our approach combines direct website measurement with established carbon intensity factors from leading sustainability research organizations.

Why Our Numbers May Appear Higher

Our carbon estimates may trend 6x higher than some other calculators because we use:

1. Conservative global grid intensity (475g CO2/kWh global average) rather than location-specific factors
2. Comprehensive measurement that includes both data transfer AND CPU processing energy
3. Real browser measurement via Puppeteer rather than page size estimation

This approach provides worst-case scenario estimates that are valuable for sustainability planning, though actual user emissions will vary significantly based on their location's energy grid.

Data Collection Process

1. Real Browser Measurement with Puppeteer

Unlike calculators that estimate based on page size alone, we use Puppeteer (headless Chrome) to:

• Load your actual website in a real browser environment
• Track every network request including images, scripts, stylesheets, fonts, videos, and third-party resources
• Measure actual resource sizes after compression and optimization
• Record real performance metrics including load times and CPU usage
• Capture Web Vitals (First Contentful Paint, Largest Contentful Paint, Cumulative Layout Shift)

2. Performance and Energy Measurement

Our analysis captures:

• Network Activity: All HTTP requests and their payload sizes
• CPU Processing Time: Main thread work and JavaScript execution time
• Rendering Work: Browser painting and layout operations
• Third-Party Impact: External scripts, analytics, and widgets
• Cache Behavior: Initial vs. subsequent page load differences

Carbon Calculation Methodology

Primary Carbon Sources

Our calculations consider two main sources of carbon emissions:

1. Data Transfer Emissions

Carbon from Data Transfer = (Total Bytes ÷ 1024) × 0.0008 gCO2e per kB

2. CPU Processing Emissions

Carbon from Processing = (Main Thread Time in seconds) × 0.0004 gCO2e per second

Total Carbon Footprint

Total CO2e per page view = Data Transfer Carbon + CPU Processing Carbon

Note: This methodology is consistently applied across data collection, storage, browser display, and PDF generation to ensure accuracy and reliability.

Carbon Intensity Factors

Our calculations use research-based carbon factors:

Energy Calculation Model

Energy Consumption = Total MB × 0.000072 kWh per MB Carbon Emissions = Energy Consumption × 475g CO2 per kWh

Why We Use Global Grid Intensity

The Trade-off: Accuracy vs. Consistency

Global Average (Our Approach):

• ✅ Provides consistent, comparable results across all websites
• ✅ Represents worst-case scenario useful for sustainability planning
• ✅ Accounts for global user base and CDN distribution
• ❌ May overestimate emissions for users in clean energy regions

Location-Based Intensity (Alternative Approach):

• ✅ More accurate for specific geographic regions
• ✅ Lower estimates in areas with clean energy grids
• ❌ Requires user location data or assumptions
• ❌ Results vary based on testing location rather than website efficiency

Regional Grid Intensity Examples

This explains why location-based calculators may show significantly lower numbers—they may be testing from regions with exceptionally clean grids.

Comparison with Other Methodologies

Website Carbon Calculator (websitecarbon.com)

• Approach: Page size estimation + regional grid factors
• Strengths: Fast, location-aware
• Limitations: Estimates rather than measures actual resources

CO2.js / Sustainable Web Design

• Approach: SWD model + location-based grid intensity
• Strengths: Well-established methodology, location-specific
• Limitations: May not capture all third-party resource impact

Our Approach

• Approach: Direct Puppeteer measurement + global grid average + CPU processing
• Strengths: Most accurate resource measurement, includes processing energy
• Limitations: Conservative global estimates, higher baseline numbers

Environmental Context Calculations

Yearly Impact Projections

We project annual environmental impact based on:

• Assumed traffic: 10,000 monthly page views (120,000 annually)
• Per-visit emissions: Measured carbon footprint
• Annual calculation: CO2 per visit × annual visits

Environmental Equivalents

Our contextual comparisons use established conversion factors:

Methodology Validation

Research Foundation

Our approach builds on established research from:

• Green Web Foundation: Carbon intensity factors and data transfer calculations
• Sustainable Web Design: Energy modeling for digital services
• International Energy Agency (IEA): Global electricity carbon intensity data
• Web Performance Working Group: Browser measurement standards

Quality Assurance

• Real browser measurement eliminates estimation errors
• Multiple carbon sources provide comprehensive coverage
• Performance-based calculations reflect actual energy usage
• Conservative estimates err on the side of environmental caution

Limitations and Considerations

What Our Calculator Includes

• ✅ All network requests and resource transfers
• ✅ Client-side CPU processing energy
• ✅ Third-party script impact
• ✅ Real browser rendering work
• ✅ Compression and optimization effects

What Our Calculator Doesn't Include

• ❌ Server-side processing energy (varies by hosting)
• ❌ Network infrastructure energy (routers, cell towers)
• ❌ Device manufacturing carbon footprint
• ❌ End-user device energy consumption
• ❌ Geographic routing and CDN specifics

Variability Factors

Real-world emissions will vary based on:

• User location and local grid intensity
• Device efficiency (newer devices are more efficient)
• Network connection type and speed
• Cache state (repeat visits use less energy)
• Time of day (grid carbon intensity varies)

Using These Estimates

For Sustainability Planning

• Use our estimates as worst-case scenarios for carbon budgeting
• Focus on relative improvements between optimized and unoptimized versions
• Consider global user base impact rather than single-location estimates

For Performance Optimization

• Larger page sizes correlate with higher emissions regardless of location
• CPU-intensive operations increase energy usage universally
• Third-party scripts add overhead that affects all users

For Reporting and Communication

• Specify that estimates use global average grid intensity
• Note that actual emissions vary by user location
• Emphasize relative improvements from optimization efforts

Continuous Improvement

We continuously refine our methodology based on:

• Latest research in digital carbon accounting
• Updated energy efficiency data from cloud providers
• Evolving web standards and measurement capabilities
• User feedback and industry best practices

Future Enhancements Under Consideration

• Optional location-based grid intensity calculations
• Server-side energy estimation integration
• Real-time grid carbon intensity data
• Industry-specific carbon factor adjustments

Questions or Feedback?

For questions about our methodology or suggestions for improvement, please reach out to our team. We believe transparency in carbon accounting is essential for meaningful climate action in the digital space.

Contact: hello@reallygood.workLast Updated: June 11, 2025Methodology Version: 1.0