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 Paint9.6 s2.0 s< 2.5 s
First Input Delay330 ms60 ms< 100ms
Cumulative Layout Shift0.0810.052 0.1


Remove autoplaying or preloaded media files

By removing 1 autoplaying or preloaded videos, roughly 10.2 MB could be removed from the page load.

This would reduce the page transfer size by 73% and reduce the pages emissions from 3.67 grams of CO2 to 0.97 grams of CO2.

Autoplaying videos can have a negative impact on the user experience for several reasons:

  1. Increased data usage: Autoplaying videos can consume a lot of data, especially if they are set to play in high definition. This can be a problem for users with limited data plans or slow connections, who may experience slow or interrupted playback.
  2. Annoyance factor: Autoplaying videos can be annoying for users, especially if they are accompanied by sound. This can lead to a negative perception of the website and decreased engagement.
  3. Reduced accessibility: Autoplaying videos can be a problem for users with accessibility needs, such as users who are blind or have hearing difficulties.
  4. Increased page load time: Autoplaying videos can increase the overall page load time, leading to a slower user experience.
  5. Decreased battery life: Autoplaying videos can consume a lot of battery power, especially on mobile devices, leading to reduced battery life.

In order to minimise the impact of autoplaying videos on the user experience, it is recommended to use them sparingly and only when necessary. It is also important to provide users with the option to turn off autoplaying videos and to allow them to control the playback of videos on the page. Additionally, videos should be optimised for performance and should be accompanied by captions or transcripts to improve accessibility.

211215_UTAS_Banner_Final.mp4 10 MB 73%

Optimise images

By optimising the following images, roughly 912 KB could be removed from the transfer size, about 6%. This would reduce the CO2 generated per page load from 3.67g grams to 3.44 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.
imas-students-binalong-bay.jpg 405 KB 3% 160 KB
students-in-hobart-city.jpg 347 KB 2% 103 KB
Engineering-students-at-SandyBay-campus.jpg 285 KB 2% 41 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.

montserrat-v15-latin-700.woff2 ~20 KB ~2 KB
montserrat-v15-latin-800.woff2 ~20 KB ~2 KB
montserrat-v15-latin-500.woff2 ~19 KB ~2 KB
montserrat-v15-latin-600.woff2 ~19 KB ~2 KB
montserrat-v15-latin-regular.woff2 ~19 KB ~2 KB
montserrat-v15-latin-300.woff2 ~19 KB ~2 KB

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.
Timing1.2 s0.4 s

Largest Contentful Paint

Timing9.6 s2.0 s

Total Blocking Time

Timing1,060 ms10 ms

Cumulative Layout Shift


Speed Index

Timing7.7 s2.5 s

Time to Interactive

Timing11.1 s2.1 s

Max Potential First Input Delay

Timing330 ms60 ms

Eliminate render-blocking resources

InsightPotential savings of 230 msPotential savings of 10 ms

Reduce unused CSS

InsightPotential savings of 42 KiB

Reduce unused JavaScript

InsightPotential savings of 478 KiBPotential savings of 476 KiB

Serve images in next-gen formats

InsightPotential savings of 1,021 KiBPotential savings of 1,021 KiB

Reduce initial server response time

InsightRoot document took 930 msRoot document took 920 ms

Avoid serving legacy JavaScript to modern browsers

InsightPotential savings of 66 KiBPotential savings of 66 KiB

Avoid enormous network payloads

InsightTotal size was 7,161 KiBTotal size was 14,251 KiB

Serve static assets with an efficient cache policy

Insight72 resources found76 resources found

Avoid an excessive DOM size

Insight1,245 elements1,245 elements

JavaScript execution time

Timing3.0 s0.4 s

Minimizes main-thread work

Timing6.0 s1.1 s

Minimize third-party usage

InsightThird-party code blocked the main thread for 820 msThird-party code blocked the main thread for 10 ms

Image elements do not have explicit width and height