A lighter site is a lower-carbon site
Web carbon numbers are usually presented with more confidence than the underlying model supports. We separate the two things: the bytes we removed, which we measured, and the emissions that implies, which is somebody else’s coefficient applied to our measurement.
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What we measured
Our own audits — the original page against the same page served through WebSpeed. The sample and the date are part of the result, not small print.
45 audited sites that cleared the publishing gates measured 2026-08-04
What this does not say. Only the bytes are ours. The grams are the Sustainable Web Design model — 0.30 kWh per GB against the global grid average — applied to those bytes, and a model is not a measurement: it averages across networks, devices and electricity grids that differ enormously, and reasonable estimates of the same transfer vary by more than a factor of two. Nor is one page load a footprint: the figure here is a single load of each site in our sample, not anyone’s monthly total, and it excludes the energy your origin and our servers spend producing the page. Treat it as a direction of travel with an order of magnitude, not as a carbon account.
What the industry benchmark says
Quoted in the unit its source used, linking the page that states it. An industry benchmark is a direction, not a forecast for one site — the per-site numbers are the audits above, and yours is a free check away.
What WebSpeed does about it
Each one is independent and can be switched off for your domain — nothing here is all-or-nothing.
Ship fewer bytes for the same page
Everything on this page follows from one thing: less data transferred. Modern image formats, subset icon fonts, stylesheets that don’t ship the whole site to draw one screen, and below-fold media that is never fetched by someone who doesn’t scroll.
Don’t fetch the same thing twice
Cached delivery means repeated requests for an unchanged page are answered without going back to your origin at all — the transfer that costs the least energy is the one that doesn’t happen.
No rebuild, no migration
The lowest-carbon version of a site improvement is the one that doesn’t require rebuilding the site. Nothing here asks you to re-platform, re-export your images or redeploy anything — the change is in delivery.
Two different kinds of number
Web carbon calculators tend to hand you a confident-looking figure in grams. The measurement underneath it is almost always the same one we make — bytes transferred — and everything after that is a coefficient.
We keep the two apart on this page because the difference is the whole story. The bytes are measured: we fetched each page as it was, fetched it as we serve it, and counted. The grams are the Sustainable Web Design model applied to that count. It is a reasonable, published, peer-reviewed-adjacent model, and it is still an average over networks, devices and electricity grids that differ by more than the effect being measured.
We also chose it knowing it is on the conservative side. Older models put emissions per megabyte several times higher, and using one of those would make our own savings look correspondingly better. That is exactly why we don’t.
What the measurement supports
Roughly half the transfer, at the median, across the sites we audited — with the count of sites that got heavier printed beside it, because on an already-lean page there is little to remove and the small runtime we add can show.
Read as energy, the claim is narrow and defensible: a page that transfers half as much data uses less energy to deliver, on the network and on the device receiving it. Read as a carbon account, it is not a claim at all — one lab load of one page per site is not anyone’s monthly footprint, and we have not measured your traffic.
The part nobody can outsource
The most effective thing on this page is also the least dramatic: not rebuilding your site.
Re-platforming, re-exporting an image library, redeploying an application — each has a real cost, environmental included, and each is what a conventional performance project asks for first. Delivery-layer optimization asks for none of it. Your site stays where it is, your images stay as they are, and the bytes on the wire halve anyway.
If your priority is emissions rather than speed, the free check still answers the useful question: how much of your page is weight nobody needed to send. It takes about a minute, and if the answer is “not much”, the report will say so.
Carbon footprint — questions
Can I put a number on my site’s footprint from this?
You can put an order of magnitude on the transfer part of it, which is what we measure. A real footprint would also include the energy your origin spends generating pages, the devices rendering them, and the grid mix wherever all of that happens. Anyone handing you a precise annual figure from page weight alone is presenting a model as an audit.
Why 0.15 g per MB — I have seen much bigger numbers?
Because the bigger numbers are usually older, or from models that allocate more of the internet’s total energy to data transfer. We use Sustainable Web Design v4 (0.30 kWh/GB against the 494 gCO₂e/kWh global average) and link it, so you can see the assumptions. It is a deliberately conservative choice: an inflated coefficient would make our own savings look better.
Is this greenwashing?
It would be if we quoted the grams and not the model, or the median saving and not the sites that got heavier. Both are on this page. The honest version of this claim is narrow — we cut transfer roughly in half on the sites we measured, and less data means less energy — and that is the version we are making.
Does a faster site help the environment more than a green host?
They are not alternatives, and a green host is the bigger and more direct lever for the energy your servers use. What page weight changes is the energy spent on the network and on every visitor’s device, which no hosting choice of yours can reach.
Pick how hands-off you want it
The before/after check is free to run; it isn’t one of these plans. Choose a plan when you’re ready to make the speed-up permanent — or buy the report once and apply it yourself.
Fast
- The whole optimization pipeline, live
- One site
- Proxy or on-site SDK, no code changes
- Cached delivery keeps your site up during origin outages
- Priced by monthly visits, scales with you
Growth
- Everything in Fast, across multiple sites
- Priority cache — your pages stay warm
- Support with a named contact
- One invoice for the whole portfolio
Custom
- Everything in Growth
- A config built by hand for your site
- What only you can change, written up for your team
- Set up, measured and maintained by us
Subscriptions start with a 14-day free trial (Fast and Growth), then run for a minimum of 6 months — you commit only after the trial. Fast is priced by monthly visits; indicative launch pricing.
Not ready for a subscription?
Buy the Audit once and apply it yourself — the same findings the pipeline acts on, written up as instructions.
- The same fixes Fast applies, written up as a guide you run yourself
- Server settings, code changes and ready-to-paste head snippets
- Before/after PageSpeed from the free check (PDF / HTML / MD)
- Re-issued free for a year as your site changes
See your own before / after
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