December 1, 2022
People expect exceptional performance when they access your site. They want quick load times, stable layouts and quick interactivity, regardless of whether they’re on desktop or mobile. To meet those expectations, you’ll need to track website performance metrics that’ll give you quick and accurate insights into how your pages perform.
However, there are a near-limitless number of ways you could try to measure web performance, and some are far better than others. These 7 website performance metrics allow you to understand how your web page performs across several different page load aspects. Some focus solely on speed and others on interactivity, but all contribute to genuinely painting an image of how healthy your pages are. By tracking these 7 metrics, you give yourself all the data you need to provide a world-class online experience that meets or exceeds your visitors’ expectations.
Largest Contentful Paint measures the size of the largest, above-the-fold element on a page when it loads. Usually, your LCP element is a large image, text or video file.
A substantial LCP element will negatively influence people’s perception of how fast your page is loading. The slower the main content loads, the more frustrating it is for visitors.
Learn more about improving your LCP in our guide to Largest Contentful Paint.
Cumulative Layout Shift measures how much visual elements move around on your page. For every element shift, a score is determined based on how much it moves and how large it is. Your final CLS is a sum of all these scores after your page has had 5 consecutive seconds with no shifting.
Everyone has experienced clicking on a page only for the page to shift, forcing you to click an unwanted ad or link. CLS issues are to blame for these kinds of frustrations. Making your website visually stable will help ensure your visitors get the web experience they’re looking for.
Learn more about improving CLS in our guide to Cumulative Layout Shift.
Total Blocking Time measures how long a page’s main thread is blocked by large tasks that take longer than 50 ms to load during the loading process. Your TBT score is calculated like a running clock, starting every time a task passes the 50 ms mark and continuing until that task is done. For this reason, it’s best to have many short tasks (less than 50 ms) rather than a few long tasks.
Visitors who interact with your site won’t perceive delays of less than 50 ms. If you keep all your tasks under this mark, your site will feel snappy and responsive, even while loading. The opposite is true, as well. If your TBT score is high, your page will feel sluggish to visitors, as their interactions take too long to process.
Learn more about improving TBT in our guide to Total Blocking Time.
Interaction to Next Paint measures the longest time a visitor needs to wait between when they interact with your page and when they get a response.
For instances of pages with fewer than 50 interactions, the INP score will be the slowest response time. For pages with more than 50 interactions, the score will be chosen from the 98th percentile of response times.
People don’t like unresponsive pages. Tracking INP allows you to find the worst offenders on your site so you can implement changes to make your website more user-friendly.
Time to First Byte measures the reaction speed of your web servers. It’s a measurement of when a visitor tries to access a page and when the first byte of data arrives.
TTFB is a great way to measure the effectiveness of your hosting and CDN choices. Poor TTFB (more than 300 ms) will delay the rendering of your page and affect other metrics. It also indicates that you might need a more effective hosting plan with servers closer to your visitors.
Learn more about improving TTFB in our guide on Time to First Byte.
Third-party scripts are code and tooling from other companies that add extra functionality to your site. Common examples of third-party scripts are Google Ads, analytics tracking code and map widgets.
Each third-party script you include adds more for that page to load. Although many third-party scripts are important for page functionality, it’s easy for pages to get bogged down with dozens of third parties inadvertently. Tracking your page’s third parties lets you be conscious of how many you’ve added so you can cut back if needed.
Learn more about identifying and managing third-party scripts.
Time to Interactive measures how long it takes for your web page to be fully interactive for your visitors. A page is considered fully interactive after the First Contentful Paint is done and the main thread has been free of long tasks (more than 50 ms) for at least 5 seconds.
Often, web performance focuses on making a page visually complete before it’s interactive for visitors. When visitors can see but not interact with a page, it leads to frustration. We should optimise pages for low TTI to ensure the best possible user experience.
Learn more about improving TTI in our guide to Time to Interactive.
Too much data can be just as harmful as not enough. For that reason, you need to ensure you’re only tracking the best possible website performance metrics. These three metrics are often tracked but should be avoided.
Getting the data you need is only the first step when you’re trying to improve your Core Web Vitals and web performance. After getting this data, you need to know how to implement it across your website and company for the best possible results.
These resources will help you take that next step toward a better web experience for your visitors:
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Engineering Manager at Google Chrome