How we calculate emissions in CLEAR

At Climate Logic, we believe in transparency and simplicity when it comes to assessing your website’s environmental impact. Our CLEAR (Carbon Load & Emissions Audit Report) tool uses a proven methodology derived from the Sustainable Web Design (SWD) principles to calculate the carbon footprint of a web page.

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Measuring Size

We Measure Data Transfer

When someone visits your website, their browser downloads content (HTML, CSS, JS, images, fonts, etc.). This content has a measurable size in bytes.

We measure the total transfer size for both:

📱 Mobile version

💻 Desktop version

Then we combine both to get a realistic picture of typical user experiences.

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Real-World behaviour

We Adjust for Real-World Usage

Not all visitors load a site the same way every time. To account for this, we apply a weighted average based on user behaviour:

75% of users are returning visitors.
25% are first-time visitors.

Returning visitors often load just 2% of the total data (due to caching).

This gives us an adjusted data transfer total per user.

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Energy per page view

We Convert Data to Energy (kWh)

Using SWD guidelines, we estimate energy used:

0.81 kWh is consumed per GB of data transferred

So we multiply the adjusted data (in bytes) by this factor to get an estimate of electricity used per page view.

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Verified data

We Convert Energy to CO₂ Emissions

Depending on the hosting environment, emissions differ.

If green hosting is detected (verified via The Green Web Foundation), we assume:

Data centre energy: 50g CO₂ / kWh
Transmission & end-user energy: 442g CO₂ / kWh

If non-green hosting is detected, we assume the entire supply chain uses grid energy:

All: 442g CO₂ / kWh

These figures are then used to calculate the CO₂ emissions per page load in grams.

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Energy per page view

We Rate Sustainability

Based on the calculated CO₂ emissions per page, your website receives a simple sustainability rating:

CO₂ per page	Rating
≤ 0.095 g	🟢 A+ (Low Impact)
≤ 0.200 g	🟢 A (Low Impact)
≤ 0.341 g	🟡 B (Moderate Impact)
≤ 0.493 g	🟠 C (High Impact)
≤ 0.656 g	🟠 D (Very High Impact)
≤ 0.846 g	🔴 E (Severe Impact)
> 0.846 g	🔴 F (Extremely High Impact)

This system is inspired by the Website Carbon methodology and makes results easy to understand.

Something to think about

We Translate Results Into Fun Equivalents

To make your results relatable, we show what your site’s emissions look like in the real world:

Number of flat whites (235g CO₂ per cup)
Number of cups of tea (7.35g CO₂ each)
Number of CO₂ balloons (16g each)
Equivalent kWh of electricity
Driving distance in a typical petrol car

These metaphors help turn abstract emissions into something tangible.

Find out how many cups of coffee your site is worth

If you’d like a more detailed audit of your site’s infrastructure, green hosting options, and performance enhancements, check out our Website Carbon Audit services or get in touch.

Check your website emissions with CLEAR