markexcell.co.uk Has Achieved an A+ Website Carbon Rating. Here Is What That Means.

markexcell.co.uk has been independently assessed by the Website Carbon Calculator and awarded an A+ rating, the highest possible grade, with a measured carbon output of 0.02g of CO2 per page visit. The site is also confirmed as running on sustainable energy.

I am sharing this not simply as a credibility note but because the result connects directly to the work this site is about. A fast, technically clean website and a sustainable website are, in most cases, the same website. The disciplines that produce one tend to produce the other, and understanding why that is the case is useful for anyone thinking about how their own site is built.

What the Website Carbon Calculator Actually Measures

The Website Carbon Calculator, built and maintained by Wholegrain Digital, estimates the carbon emissions generated each time a page is loaded. It does this by measuring the total amount of data transferred when the page loads, applying an energy intensity figure for data transfer and server processing, and then calculating the resulting carbon emissions based on whether the hosting infrastructure runs on sustainable or fossil-fuel-derived energy.

The result is an approximation rather than a precise engineering measurement, but it is a credible and widely used benchmark that allows meaningful comparison between websites. The A+ to F rating system introduced by the calculator provides a clear grading across that range, with A+ representing the cleanest tier.

What the rating means in practice

An A+ rating means the site sits in the lowest carbon tier, producing so little data per page load that the carbon output rounds to 0.0g per visit. The calculator confirmed that the site appears to be running on sustainable energy, which is the other major factor in the assessment alongside data efficiency.

To put it in context: the average web page produces around 0.5g of CO2 per visit according to Wholegrain Digital’s research. A page producing 0.0g is not simply marginally better than average; it is in a different category entirely.

Why a Sustainable Website and a Fast Website Are the Same Thing

This is the part of the result I find most interesting from a technical perspective, and the part most useful to understand if you are thinking about your own website.

The carbon footprint of a web page is determined primarily by how much data is transferred during its load. More data means more energy required to transmit it, process it and render it. Less data means less energy. The relationship is almost direct.

Now consider what makes a website fast. As covered in the image optimisation, CSS, Core Web Vitals and Google Lighthouse articles on this blog, the primary drivers of page speed are the same things that determine data efficiency: compressed and properly formatted images, lean stylesheets, minimal and well-optimised JavaScript, efficient hosting, and a codebase that does not carry unnecessary weight.

A website built with genuine care for performance is, almost by definition, one with a low carbon footprint. The same set of decisions produces the two outcomes. You do not have to choose between a fast website and a sustainable one. They are the same website.

What Contributed to the A+ Rating on This Site

The same disciplines that produced the 100/100 Core Web Vitals score discussed in the earlier article on this blog also produced the A+ carbon rating. They are not separate achievements. They are the same achievement measured by different tools.

Image optimisation

Every image on the site is properly sized, compressed and served in a modern format. No full-resolution camera files. No PNG used where WebP would be smaller. No images loading at a size larger than they are displayed. This is the single largest contributor to page weight on most websites, and addressing it properly has the biggest single impact on both performance and carbon output.

Lean CSS and JavaScript

The stylesheets on the site load only what is actually used. No large framework loaded in full when only a fraction of it is needed. No unnecessary JavaScript. No third-party scripts loading trackers, chat widgets or analytics tools that add weight without proportionate value. Keeping the code lean keeps the page light.

No unnecessary plugins or third-party embeds

Every third-party resource added to a website, whether a font loaded from an external server, a social media embed, an analytics script, or a marketing pixel, increases the data transferred on every page load. The site keeps these to a minimum, which keeps the footprint low.

Efficient hosting on sustainable infrastructure

The hosting environment matters for both performance and sustainability. Hosting on servers powered by renewable energy directly reduces the carbon intensity of every page load, regardless of how efficiently the site itself is built. The calculator confirmed this site appears to be running on sustainable energy, which is a direct result of choosing a hosting provider with a credible green energy commitment.

Why This Matters Beyond the Environment

The environmental case for sustainable web design is straightforward. The internet consumes a significant and growing amount of global energy, and the carbon footprint of digital infrastructure is a real and measurable contributor to emissions at scale. A website that minimises its data transfer and runs on sustainable energy is a small but genuine contribution to reducing that impact.

But the practical business case is equally clear. A website that produces 0.0g of CO2 per visit is also one that loads faster, scores higher on performance benchmarks, costs less to serve at scale, and provides a better experience for visitors on slower connections or older devices. The environmental and performance benefits are not in tension. They are the same outcome.

For businesses that prioritise sustainability as part of their values, a verified low-carbon website is also a genuine, credible signal to clients and customers. Unlike many sustainability claims, this one is independently verified, publicly visible and testable by anyone at websitecarbon.com.

How to Check Your Own Website’s Carbon Rating

The Website Carbon Calculator is free and publicly available at websitecarbon.com. Enter any URL, and it will return a rating and an estimated CO2 output per visit within a few seconds. The result is a useful starting point for understanding where your site sits and what the main opportunities for improvement are.

For most websites, the areas most likely to improve a poor carbon rating are the same areas most likely to improve page speed: image optimisation, reducing unnecessary scripts and third-party resources, and ensuring the hosting environment has a credible green energy commitment.

A Practical Checklist for a Lower-Carbon Website

☐  Images compressed and served in WebP or AVIF rather than unoptimised JPEG or PNG

☐  CSS kept lean, unused rules removed, no large frameworks loaded when only a fraction is needed

☐  JavaScript minimised, deferred where possible, no unnecessary third-party scripts

☐  Third-party embeds, fonts, trackers and widgets reviewed and removed where not genuinely needed

☐  Hosting provider checked for a credible renewable energy commitment

☐  Website Carbon Calculator run to establish a baseline and identify the biggest opportunities

☐  Performance tested in Google Lighthouse, since a high performance score and a low carbon score are almost always achieved together

Frequently Asked Questions

Does a low carbon rating actually make a meaningful difference to emissions?

Individually, any single website’s impact is small. At scale, it adds up—the internet as a whole accounts for a significant and growing percentage of global electricity consumption. A website receiving tens of thousands of visits a month, producing 0.0g per visit rather than the average of around 0.5g, is a meaningful difference in aggregate, particularly if more websites made the same choices. The more immediate practical benefit is to the visitors whose experience is improved by the same decisions that reduce the carbon footprint.

Is green hosting enough on its own to get a good carbon rating?

No. Hosting on renewable energy reduces the carbon intensity of the electricity used, but it does not reduce the amount of data transferred. A bloated, slow-loading website hosted on a green server is still a bloated, slow-loading website. The site’s data efficiency is the primary driver of the carbon output per visit. Green hosting improves the result further, but it cannot compensate for a poorly optimised site.

How often should I recheck my carbon rating?

Running the check after any significant change to the site is sensible, particularly after adding new plugins, third-party embeds, or making changes to images or scripts. An annual check as part of a broader performance review is a reasonable routine for sites that do not change frequently.

Can a WordPress site achieve an A+ carbon rating?

Yes. The carbon rating depends on what the site outputs to the browser, not on the platform it is built on. A well-optimised WordPress site with appropriate hosting can achieve an A+ rating just as any other well-optimised site can. The platform is not the determining factor. The build quality, the plugin discipline and the hosting choice are.

Does website carbon rating affect SEO or GEO?

Not directly, since neither Google nor AI answer engines currently factor carbon rating into their ranking or citation signals. Indirectly, the answer is yes, because a low carbon rating is almost always the result of the same technical choices that produce good Core Web Vitals scores, fast loading and lean code, all of which do contribute to search visibility. You are unlikely to have a great carbon rating and poor performance, or vice versa.

Want a Faster, Leaner, Lower-Carbon Website?

If you would like to know where your own website sits on the carbon scale and what the most impactful changes would be, get in touch for a straightforward conversation with no obligation and no sales pitch.