Methodology

How we measure what we claim.

We don't sell eco labels, we sell technical measurements. This page documents openly how our carbon estimates are produced — and where their limits lie.

The underlying model

We use the Sustainable Web Design Model (SWDM v4) from the Green Web Foundation. It weighs data transfer, end-device energy, network energy and data-centre energy. Simplified:

1 GB of transferred data ≈ 0.81 kWh ≈ 0.36 kg CO₂ (global grid mix). With an average ~2 MB per visit, that's 0.72 g CO₂.

When hosting runs on verifiably green power (Cloudflare since 2022, Google Cloud since 2017), the data-centre share is reduced — typically down to around 30 % of the total.

What we measure

  1. HTML size of the main page (gzip-compressed)
  2. Asset sizes of the top 10 images, videos, scripts and fonts
  3. Hosting provider via reverse DNS / WHOIS — matched against the Green Web Foundation list
  4. Cache headers (Lighthouse audit): returning visitors pay less
  5. Codec choice for video (AV1 vs H.264 vs VP9)
  6. Image format (AVIF vs WebP vs JPG/PNG)

What we can't measure

Honesty is part of the brand. These factors influence the real footprint but cannot be measured from the outside:

  • Server-side energy efficiency (PUE) of the actual data centre
  • Device type of the visitor (smartphone vs desktop consume differently)
  • Geographical distribution of visitors (grid mix varies by country)
  • Mobile network vs Wi-Fi share (cellular uses ~3× more energy)

We estimate with the global average and flag that transparently.

Our measurement tiers

  • Tier 1 — quick check (audit tool, free): main page plus top 10 assets. Estimate with ±30 % uncertainty. Result in ~5 seconds.
  • Tier 2 — full-site audit (290 €): crawl of all indexable pages up to 200 URLs. Lighthouse audits on 5 representative pages. ±15 % uncertainty.
  • Tier 3 — CSRD report (recurring): quarterly measurement, statistical analysis over time, audit-ready documentation. ±10 %.

Sources

Sustainable Web Design Model v4 — sustainablewebdesign.org/calculating-digital-emissions
Green Web Foundation — thegreenwebfoundation.org
websitecarbon.com methodology — websitecarbon.com/how-does-it-work
Cloudflare Sustainability Report — cloudflare.com/impact
CSRD Directive EU 2022/2464 — eur-lex.europa.eu

Quick check

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