Website Carbon and Performance Calculator
Your website is heavier and slower than you think
Heavy pages cost you three ways: enquiries lost before the page loads, weaker performance in search, classic and AI alike, and a bigger carbon and hosting bill than you need.
How it works
The Website Carbon and Performance Calculator reads one page of your website and grades it for speed, page weight and carbon emissions. The full result is on screen, nothing held back.
You give us an email address and a URL, and the grade comes back in about a minute
What it cannot tell you is whether that page is the problem or whether the whole platform is. That question needs a person, and it is what the Website Carbon and Performance Audit is for.
How website carbon emissions are measured
Emissions are estimated from how much data your page transfers, how that data moves across the network, and how the electricity powering it is generated. Heavier pages move more data, which uses more energy at every step, from the data centre to the phone in someone's hand.
The grading follows the Digital Carbon Rating System, which sets published bands from A+ down to F based on emissions per page view. Your grade is where your page sits against those bands, and against the published median for the web.
It is a model, not a meter. Nobody can measure the exact grams a single page view emits, and any tool claiming otherwise is guessing with more confidence than the science supports. What the model does reliably is tell you whether your page is heavy relative to everyone else's, and by how much.
What makes a page heavy
Most of the weight on a typical page comes from a handful of predictable places.
Images are usually first: uncompressed, larger than the space they display in, or served in formats a decade out of date. Custom fonts are next, particularly when several weights load and only two are used. Then JavaScript, both your own and everything bolted on afterwards, tag managers, chat widgets, analytics, consent tools, each one added by someone solving a real problem and none of them removed since. Video that autoplays. Third-party scripts loading further third-party scripts.
None of this is negligence. It accumulates over years of reasonable decisions, and nobody owns the total.
What the grade does not tell you
The Calculator grades one page. That is deliberate, and it is complete: you get the full result for that page with nothing withheld.
What one page cannot tell you is whether the problem is the page or the platform. A heavy homepage might be a homepage problem, or it might be a template every page on the site inherits. A slow product page might be that page's images, or it might be the hosting. The difference matters enormously, because one is an afternoon's work and the other is a platform decision.
Answering that takes reading several page types, comparing them, and having someone who has done it before work out which findings actually matter for your business. That is what the Website Performance and Sustainability Audit does.
Got questions? We’ve got answers. Don't see your answer on this list. Drop us a message
Does the Calculator store the URL I enter?
Why do you ask for an email address if the result is on screen?
Can it grade a page behind a login or on a staging site?
How accurate is the carbon figure?
Will my score change if I run it again?