Somebody taps a link. Something like half a second later, your page is there.
In that half second, a server somewhere retrieved and assembled a response; that response crossed several networks, and a device in somebody’s hand unpacked it, worked out what it meant and drew it on a screen. Three separate systems, each drawing power, none of them visible to the person who tapped.
Understanding the energy cost of a page view means following that sequence, because each stage responds to different decisions and only two of them are yours.
Energy Cost of a Page View: What Usually Gets Missed
1. The server
Your hosting draws power continuously, whether anybody is visiting or not. When a request arrives, it does additional work: querying a database, assembling a page, compressing a response.
A statically generated page requires almost none of that, since the file already exists. A page assembled fresh for every visitor requires it every time, which is what caching exists to avoid.
Renewable-powered hosting changes the emissions profile of this stage. It is commonly estimated as the smaller share of a website’s total, though the figure varies by methodology and provider.
2. the network
Every byte crosses infrastructure between your server and the visitor. Routers, exchanges, mobile base stations, all drawing power.
This scales directly with what you send. It is the most predictable stage and the one most directly under your control, since it is governed entirely by page weight.
It is also the stage where a visitor’s circumstances matter. Mobile networks are more energy-intensive per byte than fixed connections, so a heavy page costs more when delivered to somebody on a phone in a rural area, which is frequently exactly who you are trying to reach.
3. the device
The stage most often left out, and frequently the largest.
The device decompresses the response, parses the HTML, applies the CSS, downloads and decodes images and fonts, then parses, compiles and executes any JavaScript before drawing anything.
That last part is why script is disproportionately expensive. An older phone doing this work heats up and drains battery, and the visitor experiences it as the site being slow rather than as your page being heavy.
You caused that work. You do not control the device it happens on, which is a reasonable argument for restraint.
What this means for what you build
Two of the three stages are governed by what your pages contain. That is the practical conclusion.
Reduce what you send: images at display dimensions in modern formats, fonts subset and limited, third-party scripts audited, JavaScript kept to what earns it.
Reduce what has to be recomputed: cache properly so returning visitors do not re-download unchanged assets, and generate statically where the content allows.
Where performance and environmental impact both apply, treat them as the same lever: reducing unnecessary data transfer and processing supports a faster experience while lowering estimated digital carbon, though environmental figures remain modelled rather than directly measured.
Then multiply by traffic
A single page view is negligible. That is true and it is not the point.
A four-megabyte page with fifty thousand monthly views transfers substantially more than a modest page with the same traffic, and the difference compounds every month it stays unchanged.
This is why traffic-weighted measurement matters more than page weight alone. Your heaviest page is not necessarily your biggest problem; your heaviest well-visited page is.
Measuring it
Page weight, request count and Core Web Vitals on your most-visited pages, under recorded conditions, plus a carbon estimate from the same pages with a named tool.
Carbon calculators model from transfer data using assumptions about energy intensity and hosting. The Sustainable Web Design methodology documents the model most of them derive from, including how it apportions across these three stages. Different tools disagree about the same page, so use one consistently and treat the trend as more meaningful than the figure.
Anything you publish should state the tool, the conditions and the scope, since environmental claims must be accurate and substantiated.
Our website sustainability audits measure across all three stages and document the method.
