Website Carbon Footprint Calculator
How much CO₂ does your website emit?
Paste any URL and get an instant A+ to F carbon rating, based on page weight, hosting energy source, and real-world emissions factors.
URL to carbon rating in seconds
We analyze your page, measure every byte, check the hosting, and apply Sustainable Web Design Model v4. Learn more
How website carbon is calculated
A page's carbon footprint is its data transfer turned into energy, and that energy turned into emissions. Weigh everything the page downloads, multiply by the energy the internet spends moving a gigabyte, then multiply by the carbon in a kilowatt-hour of electricity. That is the whole model.
CO2 per page view equals
Carbon dioxide per page view equals page transfer in gigabytes, multiplied by 0.30 kilowatt-hours per gigabyte, multiplied by 494 grams of CO2 equivalent per kilowatt-hour.
A 1 MB page: 1/1024 GB × 0.30 × 494 = 0.145 g CO2 per view
The two fixed figures come from the Sustainable Web Design Model v4, the open methodology most digital carbon tools now use, and from Ember's global electricity data. v4 splits its 0.30 kWh/GB across the three places energy is actually spent, and separates the electricity burned at the time from the carbon already spent building the hardware:
| Segment | Operational | Embodied | Total |
|---|---|---|---|
| Data Centers | 0.055 kWh/GB | 0.012 kWh/GB | 0.067 kWh/GB |
| Networks | 0.059 kWh/GB | 0.013 kWh/GB | 0.072 kWh/GB |
| User Devices | 0.080 kWh/GB | 0.081 kWh/GB | 0.161 kWh/GB |
| Total | 0.194 kWh/GB | 0.106 kWh/GB | 0.300 kWh/GB |
Over half of it lands on end-user devices — the phone or laptop doing the rendering — which is why a lighter page helps even when your own hosting is already clean. Where the host is on renewable energy, v4 applies a lower carbon intensity to the data center share instead of the 494 gCO₂e/kWh grid average, so a green-hosted page scores better on the same bytes.
The result is an estimate, not a meter reading. It uses global averages for grid intensity and device mix, so a visitor in Norway and a visitor in Poland loading the same page do not really emit the same amount. It is built to be compared — against your last release, and against the rest of the web — rather than reported to three decimal places. The full methodology walks through each step, what changed between v3 and v4, and every source behind the numbers.
What a good score looks like
A+ means 0.040g of CO₂ per page view or less, which puts a page in the cleanest 5% of the web. Anything at or under 0.145g — a B — is comfortably better than average. The global average is about 0.36g per view, and that figure is not the middle of the scale: it is the line where F begins.
| Rating | CO₂ per page view | Where that sits | Verdict |
|---|---|---|---|
| A+ | ≤ 0.040g | Cleanest 5% of the web | Exceptional |
| A | 0.041 – 0.079g | Cleanest 10% | Excellent |
| B | 0.080 – 0.145g | Cleanest 20% | Good |
| C | 0.146 – 0.209g | Cleanest 30% | Average |
| D | 0.210 – 0.278g | Cleanest 40% | Below average |
| E | 0.279 – 0.359g | Cleanest 50% | Poor |
| F | > 0.359g | Heavier than the average page | Very poor |
The bands are deliberately unforgiving. Half of the web scores an F, because the F line was set at the weight of the average page rather than somewhere comfortable below it. A B is genuinely good; a C is better than two thirds of the sites you are competing with.
What page weight lands in which band
Because the model is arithmetic, you can place a page before you ever run it: one megabyte of transfer is about 0.148g of CO₂ per view. These are typical weights for each kind of page, converted at that rate.
| Page type | Typical transfer | Estimated CO₂ / view | Rating |
|---|---|---|---|
| Static blog or documentation page | 0.4–0.8 MB | 0.059g – 0.119g | A – B |
| Marketing landing page | 1–2 MB | 0.148g – 0.296g | C – E |
| SaaS or product homepage | 1.5–3 MB | 0.222g – 0.445g | D – F |
| Ecommerce product page | 2–4 MB | 0.296g – 0.593g | E – F |
| The average page on the web | 2.4 MB | 0.356g | E |
| News or media article | 3–6 MB | 0.445g – 0.889g | F |
| Video-heavy landing page | 5–10 MB | 0.741g – 1.482g | F |
The average page on the web transfers about 2.4 MB, which works out at roughly 0.356g per view — right on the E/F boundary. That is the single most useful thing to know about this scale: a perfectly ordinary, professionally built page is already at the bottom of it, and a B is reachable on a budget of about one megabyte.
How to reduce your site's emissions
Every gram in the result comes from bytes, so cutting emissions means cutting transfer: about 0.148g of CO₂ per megabyte you stop sending. The six changes below are in rough order of how much they tend to move the number, and all of them make the page faster at the same time — the work that lowers your carbon rating is the same work that lowers your Largest Contentful Paint.
Compress and convert your images
Images are usually the heaviest thing a page downloads. Convert to WebP or AVIF, which hold the same perceived quality in 30–50% fewer bytes, and serve a size that matches the slot with srcset instead of shipping one desktop original to every phone.
Ship less JavaScript and CSS
Minify, compress and split your bundles so a page loads only the code it uses. Unused CSS and a framework loaded for one widget cost energy in the data center, across the network and again on the visitor's device.
Move to a green host
A host running on renewable energy drops the data center portion of your emissions from the 494 gCO₂e/kWh grid average towards the renewable figure. It is the one change that lowers your result without touching a line of code — the calculator checks your host against the Green Web Foundation directory automatically.
Audit your third-party scripts
Analytics, chat widgets, social embeds, consent tools and ad tags routinely add hundreds of kilobytes that no one on the team chose deliberately. List everything loading from a domain you do not own, then justify each one or delete it.
Lazy-load anything below the fold
Images, iframes and video players that start off-screen do not need to download before the page is usable. The native loading="lazy" attribute covers most of it, and bytes a visitor never scrolls to are bytes never sent.
Cache properly and use a CDN
Correct cache headers stop returning visitors re-downloading assets that have not changed, and a CDN serves what they do need from an edge close to them. Less distance and fewer repeat transfers mean less energy for the same page.
Re-run the calculator after each change. Page weight drifts upward on its own as teams add features, images and marketing tags, so the useful habit is a measurement every quarter and after any large release — that is what catches a regression while it is still one commit rather than a year of accumulated scripts.
Offset what you cannot reduce
Some weight will not come out. Product photography, a video that earns its place, a payment script you cannot remove — at some point the page is as light as the job allows. What is left can be funded rather than ignored, as long as you are clear that funding removal elsewhere is not the same thing as emitting less here.
worked example
A page at the web's average weight, served 10,000 times a month, emits roughly 43 kg of CO₂ a year — about 94 lb. At $0.40 a pound, removing all of it costs around $38 for the year. Run the calculator on your own URL and the tool does this arithmetic against your real page weight and your real traffic.
Four things can be funded, each priced per unit with no minimum and no annual contract. Carbon removal is the direct match for a website footprint; ocean plastic and trees are what most teams pick when they want something a customer can picture.
| Impact | Price | What it funds |
|---|---|---|
| Tree planting | $0.40 per tree | Verified tree planting with GPS locations, photos and live planting sessions. |
| Carbon removal | $0.40 per lb of CO₂ | Carbon removal through direct air capture, enhanced weathering and biomass storage. |
| Ocean plastic | $0.60 per lb of ocean plastic | Ocean-bound plastic collected through Plastic Bank, about 23 bottles per pound. |
| Coral restoration | $2.20 per coral fragment | Coral reef restoration in protected waters; 15 fragments rebuild one reef structure. |
Say it accurately
Funding removal does not make a page zero-emission, and this calculator's output is an estimate from global averages rather than a measurement. “We fund the removal of an estimated 94 lb of CO₂ a year, the footprint of this site at our current traffic” is a claim you can evidence. “Carbon neutral website” is not, and in most markets it is now the kind of claim a regulator will ask you to back up. Lead with the number and the evidence, not the label.
To automate it, the Climate Action Badge turns page views into impact as they happen and links visitors to a public impact page they can check, and the REST API fires an offset from whatever event you choose.
Don't just measure — take action
Track each tangible impact in real-time. Live planting sessions, unmatched transparency.
Why does website carbon matter?
The internet produces approximately 3.7% of global carbon emissions — comparable to the entire airline industry. Every website visit requires energy: data centers process your request, networks transmit the data, and your device renders the page.
A typical web page emits around 0.36 grams of CO₂ per view. That may sound small, but multiply it by billions of daily page views worldwide and the impact becomes significant.
By measuring your website's carbon footprint, you can identify opportunities to reduce emissions through optimization — smaller page sizes, efficient code, green hosting, and optimized images all make a difference.
Want to build with our API?
Integrate website carbon analysis into your own tools, dashboards, or sustainability platforms.
View API DocumentationWebsite carbon, answered
What the number means, how it is worked out, and what to do once you have it.
It estimates the CO₂ emitted each time someone loads a web page. It weighs everything the page transfers, checks whether the host runs on renewable energy, and applies the Sustainable Web Design Model v4 emissions factors — 0.30 kWh per GB of transfer and 494 gCO₂e per kWh of electricity — to produce grams of CO₂ per view and a letter grade from A+ to F.
About 0.36g per page view, which is also where the F band begins. A page rated A+ emits 0.040g or less; anything above 0.359g is an F. What moves your own figure is page weight first, then whether the host is on renewable energy, then caching and third-party scripts.
Yes, and there is no signup. Paste a URL and you get the rating, the green hosting check and an annual estimate scaled to the monthly traffic you pick. Developers who want the same figures programmatically can use the Website Carbon API.
Version 4 of the Sustainable Web Design Model, released in July 2025. It separates operational emissions from embodied (manufacturing) emissions across data centers, networks and user devices, and applies a lower carbon intensity to the data center share when the host is verified renewable by The Green Web Foundation. The full methodology shows every step and source.
A+ (≤0.040g per view) is the cleanest 5% of the web and A (≤0.079g) the cleanest 10%. B (≤0.145g) is comfortably better than average and reachable on a budget of about one megabyte of transfer. C (≤0.209g) already beats two thirds of the web. D, E and F mean the page is carrying weight it probably does not need.
You can fund removal of what you cannot design out, which is not the same as the page emitting less. Carbon removal is $0.40 a pound, ocean plastic $0.60 a pound and trees $0.40 each, with no minimum. The Climate Action Badge can trigger it from page views, or the REST API from any event you choose.
Usually, though it is configuration rather than the platform. An unoptimized WordPress page often transfers 2–5 MB once theme assets, plugin scripts and uncached database queries are counted, which lands it in E or F. A statically generated site commonly ships 0.4–0.8 MB and scores A or B. WordPress can reach an A with aggressive image compression, a caching plugin, a CDN and a ruthless audit of installed plugins.
Marginally, and only on OLED screens, where black pixels are genuinely switched off and a dark UI can cut screen energy substantially against a bright white page. Screen energy is only a small share of per-view emissions, and on the LCD panels in most laptops and monitors the backlight stays on either way. Treat dark mode as an accessibility and battery decision; page weight, green hosting and third-party scripts move the carbon number far more.
Once a quarter, and after any significant release. Page weight creeps upward on its own as teams add features, images and marketing tags, so a quarterly check catches a regression while it is still traceable to one change. Content-heavy, media and ecommerce sites are worth checking monthly, or continuously by calling the API on a schedule.