A GreenTracer result shows two things that are easy to blur together: whether your host is listed as green, and your page's carbon rating, a letter from A+ to F. They answer different questions. The hosting listing is about where the electricity for your servers comes from. The rating is about how much data your page sends and the estimated emissions that go with it. A site can be on a green host and still get an F, or on an unlisted host and still get an A. Understanding the difference helps you choose what to fix and describe your site honestly.
What a green-hosting listing means
GreenTracer doesn't judge hosting providers itself. We ask The Green Web Foundation, a non-profit that maintains a public dataset of hosting providers that have shared evidence about the electricity they use. If your host is in that dataset, we show “Listed as green”.
The Foundation publishes what it accepts as evidence. In summary, providers publish a commitment to fossil-free energy and support it with evidence such as generating their own power, buying it directly through a power purchase agreement, being on a green electricity tariff, or buying energy certificates. The Foundation is explicit that carbon offsets cannot be used as the basis for verification, and it says it is moving from annual towards hourly matching of energy use.
What a listing does not mean:
- It is not proof of carbon neutrality. It means the provider has shared evidence of renewable energy with The Green Web Foundation. It says nothing about the provider's other emissions, or yours.
- It covers your host, not your whole page. Fonts, scripts and videos loaded from other companies run on their infrastructure, not your host's.
- It is not a GreenTracer certification. We report what the Foundation's dataset says.
How a green-hosting check works
The Foundation explains how its check works: it looks up your domain's DNS records to find the IP address the site is served from, then matches that address against the IP addresses and networks of verified providers. A domain whose address can't be linked to that evidence shows as grey.
Because the check follows the address your domain points to, a few common setups can affect the answer:
- CDNs and proxies. If your site sits behind a content delivery network, the check sees the CDN's address, not your origin server's. Your result reflects the CDN's listing.
- Resellers and agencies. If you buy hosting through an agency, the infrastructure underneath may belong to another company, and that company's listing is what counts.
- Not listed is not the same as not green. A grey result means no matching evidence was found. It may be worth asking your provider whether it has registered with the Foundation.
GreenTracer shows “Listed as green” only when the Foundation lists your host. Otherwise you will see “Not listed as green”, or “Not confirmed” if we couldn't get an answer. You can also try the Foundation's own Green Web Check.
What a website carbon rating means
GreenTracer's grade is the digital carbon rating published with the Sustainable Web Design Model v4. It grades the estimated emissions of a single page view:
| Rating | g CO₂e per page view |
|---|---|
| A+ | 0.040 or less |
| A | 0.079 or less |
| B | 0.145 or less |
| C | 0.209 or less |
| D | 0.278 or less |
| E | 0.359 or less |
| F | above 0.359 |
The grams come from your page's measured weight on a first, uncached visit, multiplied by SWDM v4's 0.300 kWh per GB and a global average of 494 g CO₂e per kWh. The rating describes one page, not your whole website or your organisation. Our explainer on what a carbon test measures and what it cannot tell you covers its limits, and the ratings page lists every band.
How the two fit together
In SWDM v4, green hosting affects only one of the six energy terms: data-centre operational energy, 0.055 of the 0.300 kWh per GB. When your host is listed as green, GreenTracer removes that term, which lowers the estimate by about 18%. Network, device and embodied energy are unchanged, because a green host doesn't change the networks your data travels over or the phones and laptops that display it.
Some worked examples using GreenTracer's model:
- 1 MB page. Not listed: 0.001 × 0.300 × 494 = 0.148 g (C). Listed as green: 0.001 × 0.245 × 494 = 0.121 g (B).
- 2.5 MB page. Not listed: 0.371 g (F). Listed as green: 0.303 g (E). Green hosting helps, but the page is still heavy.
- The A threshold. To reach 0.079 g, a page can transfer up to about 533 KB on an unlisted host (0.079 ÷ 148.2 g per GB), or about 653 KB on a listed one (0.079 ÷ 121.0 g per GB).
The takeaway: hosting can move a page across a band boundary, but page weight sets the overall level. Our guide to reducing page weight without sacrificing design covers the other lever.
Side by side
| Green-hosting listing | Carbon rating | |
|---|---|---|
| Question it answers | Has the host shared evidence of green energy with The Green Web Foundation? | About how much CO₂e does one first visit to this page cause? |
| Based on | The provider's evidence and the IP address your domain points to | Measured page weight and SWDM v4 averages |
| Covers | Your hosting provider | One page, including third-party files |
| Does not prove | Carbon neutrality, or anything about third parties | Your site-wide or company footprint |
| How you change it | Choose or ask a provider that is listed | Send less data; a listed host lowers it about 18% |
What to do next
- Check both labels for your main pages. Start with your home page and your most visited pages.
- If your host isn't listed, ask why. Ask your provider, and your CDN if you use one, whether they are registered with The Green Web Foundation. If you are choosing a new host, check it first.
- Work on page weight either way. It affects every term in the estimate, not just the data-centre one.
- Describe each label precisely. “Our host is listed as green by The Green Web Foundation” and “This page is rated B under SWDM v4” are both accurate. “Our website is carbon neutral” is not something either label supports.
- Keep it current. Hosting arrangements and pages change, so recheck after a migration or redesign. If you display a GreenTracer badge, it uses the same hosting wording.
Check your page
Run a free GreenTracer check to see your page's hosting status, estimated CO₂e per visit and rating side by side. For the full calculation, read how it works or the FAQ.
Sources
- The Green Web Foundation: What we accept as evidence of green power
- The Green Web Foundation: How does the Green Web Check work?
- The Green Web Foundation: Green Web Check
- Sustainable Web Design: Estimating Digital Emissions (SWDM v4)
- Sustainable Web Design: Digital Carbon Ratings
- The Green Web Foundation, CO2.js: Methodologies for calculating website carbon