Website Carbon Calculator
CO2e per page view and per year, its rating, and where the page weight goes.
Free preview.
- Free preview: the rating, the page weight and the first rows of each table and list (up to 10), with the CO2e and energy amounts hidden.
- Locked until you unlock it: download and copy.
- Unlock: Pro pass, ₹179 for 30 days, a one-time payment that never renews.
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Estimate a page’s carbon
Carbon estimate
Where the emissions come from (per view)
| Part | Operational | Embodied | Total | Share |
|---|
What if the page were lighter?
Where the weight goes
| Type | Files | Size | Share |
|---|
Ways to cut it
Measured files
| File | Type | Size | Notes |
|---|
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About the Website Carbon Calculator
Every page view moves data through data centres, networks and the visitor’s device, and all three use electricity and hardware. This calculator turns a page’s weight into an estimate of its emissions with the Sustainable Web Design Model (version 4), an open model that many website carbon calculators use: grams of CO2e per page view, per month and per year for your traffic, the energy behind it, and the model’s Digital Carbon Rating from A+ to F.
Enter a page address and the page is measured: its HTML and the scripts, stylesheets, fonts, images and frames it references, each asked for its size without being downloaded, with the host checked for green energy with The Green Web Foundation. Or enter the weight yourself from your browser’s developer tools. Then see where the weight goes and what cutting it would save, with every assumption shown.
How to use it
- Choose Measure a page and enter the address, or Enter the page weight and type the transfer size (in Chrome, Edge or Firefox: open the developer tools, choose Network, reload the page and read the “transferred” total at the bottom).
- Enter your page views a month. Open Model settings to set returning visitors and caching, a local electricity grid intensity, or green hosting your provider confirms.
- Press Calculate. The result shows grams of CO2e per page view with its rating, the totals for a month and a year, and how the estimate splits between data centres, networks and devices.
- For a measured page, read Where the weight goes and Ways to cut it: each saving says what it assumes and what it would save a year at your traffic.
- Without a pass the result is a free preview: the rating, the page weight and the first rows of each table, with the CO2e and energy amounts hidden. With a Pro pass you see every figure and can copy the summary or download the report and the list of measured files as CSV.
Examples
Page weight 2.4 MB · 10,000 page views a month · not green hosted
≈ 0.356 g CO2e per view (rating E) · ≈ 3.56 kg a month · ≈ 42.7 kg a year
2.4 MB × 0.3 kWh/GB × 494 g/kWh. The rating scale puts the median page of its HTTP Archive data at about 2.4 MB, the boundary between E and F.
Page weight 2.4 MB · green hosting 100%
≈ 0.29 g CO2e per view
Green hosting removes only the data centres’ operational share (0.055 of the 0.3 kWh per GB); networks, devices and hardware still count.
Common uses
- Adding a carbon estimate and rating to a sustainability report, an impact page or a client proposal, with the method stated.
- Comparing the before and after of an image, font or script clean-up in grams and kilograms a year.
- Checking whether a host is recognised as green by The Green Web Foundation.
- Showing a team where a page’s weight goes, file by file, and which fixes save the most.
How the estimate is worked out
The Sustainable Web Design Model v4 uses data transfer as a proxy for the energy a page view uses, per gigabyte (1 GB = 10^9 bytes):
- operational energy: data centres 0.055 kWh/GB, networks 0.059 kWh/GB, user devices 0.080 kWh/GB;
- embodied energy (making the hardware): data centres 0.012, networks 0.013, user devices 0.081 kWh/GB;
- in all 0.3 kWh/GB, multiplied by the grid’s carbon intensity: the global average of 494 g CO2e/kWh unless you set your own.
A green hosting factor (0 to 1) removes that share of the data centres’ operational emissions. Returning visitors download only what is not in their cache: per view = S × new visitors + S × returning visitors × (1 − cached share), where S is the sum above. Local grid intensities apply to the operational parts only; the model keeps the global figure for embodied emissions, because hardware supply chains are worldwide.
The rating
The Digital Carbon Ratings grade grams of CO2e per page view: A+ up to 0.040 g, A up to 0.079 g, B up to 0.145 g, C up to 0.209 g, D up to 0.278 g, E up to 0.359 g and F above. The grades follow the 5th, 10th, 20th, 30th, 40th and 50th percentiles of page weight in the HTTP Archive data the scale was built from, so A+ to E cover the lightest half of the web and F means heavier than the median page. The rating here always uses the global grid intensity, so it compares pages fairly wherever their visitors are.
What a measurement counts
The page’s HTML (its compressed size where the server compresses it) and the files the HTML names: stylesheets, scripts, preloaded fonts, one image per <img> (the one a browser would pick by default), posters, backgrounds in style attributes, the favicon and embedded frames (their own page only). Each file is asked for its size with a HEAD request; nothing is downloaded. Not counted: files loaded by stylesheets (web fonts, background images) and by scripts (ads, analytics, lazy loaders), video and audio (downloaded when played), and files whose server does not say their size. For an exact total, use the “transferred” figure from your browser’s developer tools in Enter the page weight.
Green hosting
In URL mode the page’s host name is checked with The Green Web Foundation’s Greencheck API, which lists hosting providers that have shown they run on green energy. A listed host gets a green hosting factor of 1, as the model suggests for hosts the Green Web Foundation confirms; you can change it under Model settings, for example to the renewable share your provider publishes. Not being listed does not prove a host is not green: it may not have applied.
Limitations
- It is an estimate from data transfer with average figures, not a measurement of the real electricity your servers, networks and visitors use. Two calculators with different models or settings give different numbers; compare pages with the same settings.
- A measurement sees only the files named in the HTML, so the real page weight is usually higher (fonts and images loaded by CSS, scripts and what they load). Use the browser’s developer tools for the full figure.
- Sizes come from the Content-Length each server reports. A file without one is listed as unknown and not counted.
- Results apply to one page; other pages of the site can weigh much more or less.
- Each visitor can run a limited number of measurements per hour (one measurement makes several server requests), which keeps the service within its hosting limits. Entering the weight by hand makes no server request.
Privacy
In “Measure a page” mode the page address and the addresses of the files it references are sent to MySmartCoPilot’s server, which requests them from the website, and the host name is checked with The Green Web Foundation. MySmartCoPilot does not store the addresses or the results, and the server log records only the host name, status code and time of each request, never the full URL or your IP address. “Enter the page weight” sends nothing.
Frequently asked questions
What do I get without a pass?
Without a pass, Website Carbon Calculator shows the rating, the page weight and the first rows of each table and list (up to 10), with the CO2e and energy amounts hidden. Until you unlock it, the result can’t be downloaded or copied. A Pro or Premium pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
How much CO2 does a website produce?
With the Sustainable Web Design Model, about 148 g of CO2e per gigabyte transferred at the global average grid intensity, so a typical 2 to 3 MB page is roughly 0.3 to 0.45 g per view. Multiply by your page views: at 10,000 views a month a 2.4 MB page is about 43 kg a year. Lighter pages, caching and green hosting all reduce it.
Why does green hosting not bring the figure to zero?
Because in the model the data centre is only part of the picture: green hosting removes the data centres’ operational emissions, but networks, visitors’ devices and the embodied emissions of all the hardware remain. Making the page lighter reduces every part.
Should I count returning visitors and caching?
If you know your share of returning visitors and that your files are cached, yes: set both under Model settings and the estimate lowers the transfer for those visits. The model gives no defaults, so the calculator starts with every visit as a first visit, which is also what the rating scale assumes.
Which grid intensity should I use?
The global average (494 g CO2e/kWh, from Ember’s data, as the model uses) is the default and keeps results comparable. If your servers and visitors are mostly in one country, you can enter that country’s grid intensity for the data centre and for visitors; Ember (ember-energy.org) and national energy agencies publish them. The model recommends keeping the global figure for embodied emissions, which the calculator always does.
Why is my measured page weight lower than in my browser’s developer tools?
The measurement counts only the files the HTML names, and only those whose server reports a size. Fonts and images loaded by stylesheets, and anything scripts add, are left out. Enter the developer tools’ “transferred” total in Enter the page weight for the full figure.