Website carbon calculator
Website carbon calculator
Run a free web carbon calculator check on any URL and see your website carbon footprint in seconds — estimated CO2 per pageview, page weight and Google Lighthouse PageSpeed scores. Then get the WordPress-focused fixes that make the site faster for visitors, stronger in organic search and lighter on emissions.
Free homepage test with a trial account. Results are modelled estimates, not measurements.
Example verification
CarbonVerifiedCarbon VerifiedCV-2025-0142 · valid to 2026-11-04- Estimated CO2 / pageview
- 0.34 g
- Reduction vs baseline
- 41%
- Average page weight
- 812 KB
- Sustainability score
- 81 / 100
These figures are modelled estimates and should not be interpreted as direct measurements of electricity use or greenhouse gas emissions.
What we measure
What the website carbon footprint calculator measures
Every result comes from a live scan, not a survey. The website carbon footprint of a page comes down to how much data it moves and how that data is powered, so each check reports the webpage CO2 emissions estimate alongside the performance numbers behind it.
Estimated CO2 per pageview
Grams of CO2e for a single visit, modelled from the data your page transfers and published energy-intensity figures.
Page weight and requests
Total transfer size in KB plus the number of HTTP requests, broken down by images, JavaScript, CSS, fonts and third-party scripts.
Lighthouse PageSpeed scores
Live Performance, SEO, Accessibility and Best Practices categories, with Core Web Vitals: LCP, INP and CLS.
Green hosting signal
Whether the domain resolves to a host that reports renewable energy, which lowers the data-centre share of the estimate.
Website CO2 calculator grade
An A-to-F efficiency grade, so your website CO2 calculator result is directly comparable with a typical website.
These figures are modelled estimates and should not be interpreted as direct measurements of electricity use or greenhouse gas emissions.
Method
How the web carbon calculator works
A website CO2 calculator is only as good as the data behind it. Ours uses a live page load rather than assumptions, and we publish the conversion factors we apply.
- 01
Enter your domain
No account, no plugin, no analytics access. Unlike a survey-style carbon calculator website, any publicly reachable URL works, including your competitors'.
- 02
We run a live scan
Google PageSpeed Insights loads the page and reports real transfer size, request counts, Lighthouse categories and Core Web Vitals.
- 03
We model the emissions
Transferred bytes are converted into estimated website carbon emissions per pageview across data centre, network and device, adjusted for green hosting.
- 04
You get a graded result
An efficiency grade, annual impact estimate at your traffic level, and the specific fixes that would cut both load time and emissions.
Breakdown
What your website carbon footprint is made of
Four factors drive the estimate. A carbon calculator website that asks you to fill in a form can only guess at them; a live scan reads most of them directly.
Data transfer
The bytes your page sends over the wire — images, JavaScript, CSS, fonts and third-party scripts. Usually the single biggest lever.
Hosting energy mix
How the data centre serving your site is powered. Renewable supply lowers the data-centre share of the estimate, not the page weight.
Visitor devices
The energy visitors' phones and laptops use rendering your pages. Heavier pages and more scripts mean more device work.
Traffic volume
Per-pageview figures scale with monthly visits, which is how a small saving per page becomes a meaningful annual one.
That is why two sites with identical designs can report very different website carbon emissions.
How it works
Speed first. Carbon verified.
We audit your WordPress site like a Lighthouse report, prioritise the fixes that move the needle, and verify the work with evidence. Each stage has to be completed before the next one becomes available.
- 01
Add your WordPress site
Create an account, add your domain and confirm ownership with a DNS record, meta tag or file upload.
- 02
Run a PageSpeed assessment
We model page weight, requests and asset bloat to produce a Lighthouse-style performance score and an estimated carbon figure per pageview.
- 03
Work the action plan
Prioritised speed fixes — image compression, script reduction, caching, hosting — each with estimated page-weight and carbon savings.
- 04
Submit for review
Upload evidence of the improvements you completed. An independent reviewer verifies your faster, leaner website.
Where to go next
Guides to reducing website carbon emissions
The calculator tells you where your website stands. These take you through what to actually change — PageSpeed, hosting and sustainable web design.
WordPress speed optimisation
What slows WordPress down, what we fix, and how the PageSpeed gains lower estimated emissions too.
Read the WordPress speed guideWordPress SEO audit
Lighthouse scores, Core Web Vitals and page weight, with the fixes for LCP, CLS and INP.
Read the WordPress SEO audit guideCost of a slow website
Model how bounce rate climbs with each fraction of a second, and the revenue a faster load time recovers.
Open the slow website cost calculatorSustainable web design
How to build an eco friendly website: techniques ordered by impact, plus page weight benchmarks.
Read sustainable web design techniquesGreen web hosting
What green hosting claims actually prove, and how much of your footprint your host controls.
Read the green web hosting guideVerification levels
Beyond a carbon footprint website calculator: independent verification
A carbon footprint website calculator gives you a number. Verification confirms you actually reduced it, reviewed by a person against evidence you supply.
Carbon Measured
Baseline PageSpeed and carbon assessment completed. You know your Lighthouse scores, Core Web Vitals gaps and estimated emissions per pageview.
Carbon Committed
A measurable speed and carbon reduction plan is in place, with owners, due dates and target improvements to page weight and load time.
Carbon Reduced
Implemented improvements have cut page weight, requests and estimated emissions against the baseline. Before-and-after data is recorded.
Carbon Verified
Full PageSpeed and carbon assessment completed, supporting evidence submitted and independently reviewed. Badge valid for twelve months.
Credibility
What we will never say about your website
We lead with speed and search performance because those are measurable business outcomes. Our carbon language is deliberately narrow, and our badge only ever states what was reviewed.
- “Carbon neutral”, “net zero” or “zero carbon” website
- That a purchase, subscription or donation grants verification
- That offsets cancel out your website's estimated emissions
- That our modelled estimates are measurements of actual electricity use
What verification does state
- Scope. Estimated emissions from website data transfer only, for the named domain.
- Baseline. A dated assessment with a published methodology version.
- Evidence. Improvements that a reviewer checked against supporting documents.
- Term. Twelve months, after which the record expires unless renewed.
These figures are modelled estimates and should not be interpreted as direct measurements of electricity use or greenhouse gas emissions.
Pricing
A free carbon footprint calculator website, paid optimisation work
Checking is free with a trial account. Plans from £5 a month cover monitoring, action plans and verification.
Starter
£5
per month
Homepage-only PageSpeed and carbon monitoring for a single WordPress site.
Essential
£39
per website / month
Full PageSpeed and carbon assessments, prioritised fixes and progress tracking.
Professional Verification
£249
per month
Independent reviewer assessment of your speed and carbon improvements.
Agency Partner
From £499
per month
Manage PageSpeed and carbon verification across a portfolio of client websites.
Common questions
Website carbon calculator FAQs
Try the website carbon calculator
Get your estimated CO2 per pageview, page weight and Lighthouse PageSpeed scores in under a minute, then decide whether to take it through the full assessment and review process.