Understanding the carbon impact of your website is one of the most practical steps you can take toward reducing your organisation’s digital footprint. The good news is that you don’t need specialist software or a technical team to get started. With GA4, a spreadsheet, and WebsiteCarbon.com (which uses the Sustainable Web Design Model), you can produce a solid annual CO₂e estimate for your site.

But first, what even is CO₂e?

CO₂e stands for carbon dioxide equivalent. It’s a standard unit used to compare the warming impact of different greenhouse gases by expressing them all as the amount of CO₂ that would have the same effect. Even though websites don’t emit CO₂ directly, the electricity used to power servers, data centres, networks, and user devices does, and CO₂e is how we quantify the impact.

1. Export one year of pageview data from GA4

The goal is to understand which pages on your site generate the most traffic. These pages contribute the most to your website’s carbon footprint, because they’re downloaded to users’ devices more often.

Step-by-step in GA4

1. Open Google Analytics 4 and select the correct property.
2. Go to Reports → Engagement → Pages and screens.
3. In the top-right, set the date range to the last 12 months.
4. Make sure the table is showing the Views column (this is pageviews in GA4).
5. Click the Share icon (top right) and choose Download → Download CSV.
6. This gives you a raw export of every page viewed in the past year.

2. Prepare your spreadsheet

1. Open the downloaded file in your spreadsheet tool of choice.
2. Sort the data by Views (descending). The most visited pages should appear at the top — these are the ones we’ll measure directly.
3. Identify the top 10–20 pages, depending on how deep you want your dataset to be.

3. Add two new columns

Add these columns directly after the pageviews column:

• CO₂e per page view
• Annual CO₂e

We’ll fill them in shortly.

4. Measure your most popular pages on WebsiteCarbon.com

Visit websitecarbon.com.

For each of your top pages:

1. Copy the full URL from your spreadsheet.
2. Paste it into the Website Carbon calculator.
3. Run the test and note the value labelled “…g of CO₂ per view”.
4. Paste that number back into your CO₂e per page view column.

Repeat this for all 10–20 pages. The more pages you measure, the more accurate your final estimate will be.

5. Calculate the annual CO₂e for each popular page

In the Annual CO₂e column, add a formula to multiply: CO₂e per page view × annual pageviews

Copy that formula down the column so that each of your measured pages now shows the annual emissions attributed to that page.

6. Estimate the carbon for the remaining pages

You likely have many pages beyond the top 20 — and most of them won’t be worth measuring individually. Instead, we take an average.

How to calculate the average CO₂e per pageview

1. Take the mean of the CO₂e per page view values from your measured pages.
2. Add up the total annual pageviews for all the unmeasured pages.
3. Multiply those two numbers: Average CO₂e per pageview × total pageviews of remaining pages

This gives you a reasonable estimate based on real data, following the Sustainable Web Design Model.

7. Add everything up

To get your total footprint:

1. Add together the annual CO₂e for all directly measured pages.
2. Add the estimated annual CO₂e for the unmeasured pages.

The total is your estimated annual greenhouse gas emissions (in CO₂e) for your website.

This number becomes the baseline against which you can measure improvements in performance, efficiency, or hosting.

8. Finding real-world equivalents for CO₂e

For reporting your findings, it might be useful to translate grams or kilograms of CO₂e into something people intuitively understand. Here are reputable sources you can cite:

• UK Government GHG Conversion Factors — Real-world comparators like passenger-vehicle miles or electricity use.
• Carbon Footprint Ltd – Carbon Comparisons — Clear visual equivalents for everyday activities. (Link)
• US EPA Greenhouse Gas Equivalencies Calculator — Includes miles driven, energy use, waste, and more. (Link)

These tools help you communicate the impact in human terms.

What next?

This method isn’t a full lifecycle assessment, but it is a reliable, transparent way to understand and benchmark the emissions of your website using the Sustainable Web Design Model.

By repeating this process annually, you can track whether your emissions are going up or down, identify high-impact pages, prioritise optimisation work and make meaningful improvements to your digital carbon footprint.

Long term monitoring

For an even more in-depth understanding of your website's CO₂e, you might consider using digitalcarbon.online — a paid service that measures  all of your emissions against pageviews automatically, so you can see your emissions go up and down in response to your efforts.

Owen Matthews, Director, Ten4Design