Google Lighthouse Performance

The Google Lighthouse performance score is a metric that measures the speed and performance of a website. It’s an overall score that ranges from 0 to 100 and is generated based on a number of different performance metrics, such as the time it takes for a website to load, the time it takes for a website to become interactive, the size of the resources used by the website, and other factors that impact the user experience.

A high performance score in Google Lighthouse indicates that a website is fast and responsive, which can lead to a better user experience and improved search engine rankings. On the other hand, a low performance score can indicate that a website is slow and unresponsive, and can negatively impact the user experience.

Mobile Performance
Desktop Performance

Core Web Vitals

Core Web Vitals are a set of specific factors that Google considers important in a webpage’s overall user experience. Core Web Vitals are made up of three specific page speed and user interaction measurements: Largest Contentful PaintFirst Input Delay, and Cumulative Layout Shift.

Largest Contentful Paint28.8 s4.7 s< 2.5 s
First Input Delay330 ms200 ms< 100ms
Cumulative Layout Shift0.0970.174 0.1

Tracking scripts

All the tracking scripts on the site generated ~1 MB of data

A tracking script is a code snippet designed to track the flow of visitors who visit a website. Media, advertising, and analytics organisations will provide a script to add to your website that sends data directly to their servers. This data can then be used to measure goals and conversions, analyse user behaviour, and influence advertising campaigns.

Consider how much of this data you actually need and use? How often do you review the analytics data, and does this inform genuine change? Are you actively running social media campaigns? Consider pausing or removing tracking scripts that aren’t being actively used. 6 489 KB 2 100 KB 6 494 KB 5 44 KB 7 27 KB 4 8 KB 2 10 KB 4 49 KB 5 3 KB 3 0 B 2 582 B 2 2 KB 1 1 KB 6 1 KB 1 457 B 3 2 KB 6 1 KB


Optimise images

By optimising the following images, roughly 938 KB could be removed from the transfer size, about 20%. This would reduce the CO2 generated per page load from 1.02g grams to 0.81 grams.

Images should be optimised for the web for several reasons:

  1. Reduced file size: Optimizing images can result in a smaller file size, which can help to reduce the amount of data that needs to be downloaded. This can lead to faster page load times and improved performance.
  2. Improved user experience: Optimising images can help to improve the overall user experience, as pages with optimised images load faster and are more responsive.
  3. Lower emissions: Optimising images can help to reduce the emissions associated with data transfer, as less data needs to be transmitted over the network.
  4. Better accessibility: Optimising images can make them more accessible to users with slower connections or limited data plans.
STC01896_Autumn23-FeatureBanner_v1-copy.jpg.aspx 1 MB 23% 918 KB
drtv_hpslider.jpeg.aspx 123 KB 3% 20 KB

Subset large font files

Fonts should be subsetted to reduce the file size, improve performance, and reduce emissions. Subsetting a font involves removing any characters that are not needed for a particular use case, resulting in a smaller file size and faster page load times. Some specific reasons why fonts should be subsetted include:

  1. Reduced file size: Subsetting a font removes any unused characters, which can result in a smaller file size. This can help to reduce the amount of data that needs to be downloaded, leading to faster page load times and lower emissions.
  2. Improved performance: Fonts that are subsetted are faster to load and render than fonts that are not subsetted. This can help to improve the overall performance of a website, leading to a better user experience.

Overall, subsetting fonts is a good practice for anyone looking to optimize the performance and reduce the emissions of a website of a website.

Lato-Regular.ttf ~82 KB ~64 KB
Lato-Bold.ttf ~80 KB ~63 KB
Oswald-Medium.woff ~80 KB ~62 KB
Lato-Regular.woff ~80 KB ~62 KB
Lato-Bold.woff2 ~80 KB ~62 KB
Lato-Regular.woff2 ~80 KB ~62 KB
Oswald-Medium.woff2 ~80 KB ~62 KB
Lato-Bold.woff ~80 KB ~62 KB
Oswald-Medium.ttf ~71 KB ~54 KB

Convert font files to woff2

WOFF2 is considered to be the best font format for web use because it provides a good balance of file size and compatibility. Some specific reasons why WOFF2 is a good font format include:

  1. Small file size: WOFF2 is a compressed font format, which means that it has a smaller file size compared to other font formats like TTF or OTF. This is important for web use because smaller file sizes can help to reduce the amount of data that needs to be downloaded, leading to faster page load times.
  2. High-quality font rendering: WOFF2 provides high-quality font rendering, making it a good choice for use on the web.

It’s worth noting that WOFF2 is not the only font format that can be used on the web, and there may be cases where other formats like WOFF or TTF are more suitable, depending on the specific requirements of the website. However, for most cases, WOFF2 is considered to be the best font format for web use due to its combination of small file size, good browser support, and high-quality font rendering.


First Contentful Paint

First Contentful Paint (FCP) is a performance metric that measures the time it takes for the first piece of content to be rendered on the screen when a user navigates to a web page. This content can be any visual element on the page, such as text, images, or a background color.

FCP is important because it directly affects the perceived speed of a website, and can impact user engagement and conversion rates. A faster FCP can lead to a better user experience and improved performance.

Here are a few ways you can optimise your FCP:

  1. Optimise images: Large, unoptimised images can slow down a page’s FCP. You can optimise images by compressing them, reducing their dimensions, and choosing the right format for each image.
  2. Minimise HTTP requests: Each resource requested by a web page, such as images, scripts, and stylesheets, requires a separate HTTP request. Minimising the number of HTTP requests can help to reduce the time it takes for a page to render.
  3. Prioritize critical content: Prioritizing critical content, such as above-the-fold content, can help to ensure that users see something on the screen quickly, even if the rest of the page is still loading.
  4. Reduce server response time: A slow server response time can significantly impact FCP. Optimizing server-side code and server settings can help to reduce response times and improve FCP.
  5. Use a performance monitoring tool: There are many tools available that can help you monitor your website’s performance, including FCP. These tools can help you identify performance issues and track your progress as you implement optimizations.
Timing5.4 s1.7 s

Largest Contentful Paint

Timing28.8 s4.7 s

Total Blocking Time

Timing1,650 ms140 ms

Cumulative Layout Shift


Speed Index

Timing13.6 s5.2 s

Time to Interactive

Timing20.0 s4.3 s

Max Potential First Input Delay

Timing330 ms200 ms

First Meaningful Paint

Timing5.4 s1.7 s

Eliminate render-blocking resources

InsightPotential savings of 300 msPotential savings of 540 ms

Properly size images

InsightPotential savings of 27 KiB

Defer offscreen images

InsightPotential savings of 102 KiB

Minify JavaScript

InsightPotential savings of 14 KiBPotential savings of 10 KiB

Reduce unused CSS

InsightPotential savings of 52 KiBPotential savings of 37 KiB

Reduce unused JavaScript

InsightPotential savings of 634 KiBPotential savings of 661 KiB

Efficiently encode images

InsightPotential savings of 782 KiBPotential savings of 782 KiB

Serve images in next-gen formats

InsightPotential savings of 938 KiBPotential savings of 938 KiB

Enable text compression

InsightPotential savings of 18 KiBPotential savings of 18 KiB

Reduce initial server response time

InsightRoot document took 860 msRoot document took 1,210 ms

Avoid enormous network payloads

InsightTotal size was 4,581 KiBTotal size was 4,580 KiB

Serve static assets with an efficient cache policy

Insight34 resources found33 resources found

Avoids an excessive DOM size

Insight752 elements676 elements

Reduce JavaScript execution time

Timing6.9 s1.9 s

Minimize main-thread work

Timing9.6 s2.8 s

Ensure text remains visible during webfont load


Minimize third-party usage

InsightThird-party code blocked the main thread for 1,310 msThird-party code blocked the main thread for 80 ms

Does not use passive listeners to improve scrolling performance


Image elements do not have explicit width and height