Every page view uses electricity: in the data centre that serves it, in the networks that carry it and on the device that displays it. Offsetting a website means estimating that energy, converting it to CO₂e and retiring credits for it. The catch is that the estimates are far less certain than for a flight or a car. This page is part of our guide to offsetting.
How are website emissions estimated?
Most website carbon calculators use the same basic method: estimate the data a site transfers, multiply by an energy intensity in kWh per gigabyte, then multiply by the carbon intensity of electricity. The most widely published version is the Sustainable Web Design Model, now at version 4Source 1.
Version 4 splits the energy per gigabyte into three parts, each with an operational and an embodied figureSource 1:
Scrolls sideways to show every column.
| Segment | Operational (kWh/GB) | Embodied (kWh/GB) |
|---|---|---|
| Data centres | 0.055 | 0.012 |
| Networks | 0.059 | 0.013 |
| User devices | 0.080 | 0.081 |
As of Oct 2026 · Source: [1] Sustainable Web Design Model v4
Added together, that is 0.30 kWh per gigabyte. The model’s default carbon intensity is the global average for electricity, 494 g CO₂e per kWhSource 1, which gives about 148 g CO₂e per gigabyte transferred.
Matched shop
Buy portfolio credits
- Registry serial numbers
- Retirement certificate
- Project documentation
A worked example
Take a made-up site with an average page weight of 2 MB and 50,000 page views a month. That is about 1,200 GB a year. At 0.30 kWh per GB it uses about 360 kWh, and at 494 g per kWh it comes to about 178 kg of CO₂e a year, or under a fifth of a tonneSource 1. One credit would cover it.
The full model then adjusts this figure. Returning visitors load cached files from their own device, so the model applies a returning-visitor and cache ratio, and a green hosting factor can reduce the data-centre part for hosts that use renewable or zero-carbon powerSource 1. Both bring the estimate down.
Your hosting or CDN dashboard may show the total data transferred directly, which is more accurate than multiplying page weight by page views.
How uncertain is it?
Treat the result as a rough estimate
The model’s authors say that by using broad system boundaries, its results are likely to overestimate actual emissions, and that models like it will always under- or overestimateSource 1. Peer-reviewed work shows how wide the range is: published estimates of the electricity used to transmit data over the internet varied by up to five orders of magnitude for 2000 to 2015Source 2.
The same study estimated 0.06 kWh per GB for fixed-line networks in 2015, and found that this figure had halved about every two years since 2000 in developed countriesSource 2. Network efficiency keeps improving, so a kWh-per-GB figure ages quickly. Use a current model version, say which one you used, and offset the higher figure if in doubt.
Cut what you can first
The Oxford Offsetting Principles start with reducing emissions and treat credits as a complement for what remainsSource 4. Because the estimate scales with data transferred, the most effective cuts make pages lighter:
- Compress and resize images, and use modern formats.
- Avoid autoplay video and load media only when it is needed.
- Remove unused scripts, fonts and third-party tags.
- Cache static files so returning visitors don’t download them again.
- Choose an efficient host that powers its data centres with renewable electricity.
Lighter pages also load faster, which helps visitors on slow connections.
How to offset a website, step by step
Step 1: Find your data transfer
Take the yearly page views from your analytics and the average page weight, or the total data transferred from your hosting or CDN dashboard.
Step 2: Convert to energy and CO₂e
Multiply the gigabytes by a kWh per GB figure from a published model, then by a grid carbon intensity.
Step 3: Cut what you can
Compress images and video, remove unused scripts, cache static files and choose an efficient host.
Step 4: Work out how many credits you need
One credit covers one tonne of CO₂e, so round the yearly estimate up to whole credits.
Step 5: Buy from a seller you can check
Choose a seller that names the project, standard and registry before you pay.
Step 6: Confirm the retirement
Look up the serial numbers in the public registry and keep the record with your estimate.
One credit represents one tonne of CO₂eSource 5. Our credits calculator rounds your estimate up and shows an estimated cost.
Where a website fits in a company footprint
For a business, the website is usually a small part of a bigger footprint. Hosting and software you buy in fall under scope 3, category 1, purchased goods and servicesSource 3, alongside everything else the company buys. If you are offsetting for a company, measure travel, shipping and purchased goods too; see our guides to offsetting business travel and offsetting e-commerce shipping, and the small business buying guide.
Claims: what an offset can and can't say
A “carbon neutral website” badge is a claim about your business, not just your site. In the EU, from 27 September 2026, claiming that a product has a neutral, reduced or positive greenhouse gas impact because of offsetting is banned in consumer marketingSource 6. A statement of what you measured, which model you used and the credits you retired, with a link to the registry record, is safer and more useful.