Introduction to Core Web Vitals

Created by Paul Williamson, Modified on Mon, 9 Oct, 2023 at 3:16 AM by Paul Williamson

the user remains on the page and interacts with your content. Currently, most websites perform well on FID measurement.

Note

Zooming and scrolling are not measured for FID.

LCP

LCP measures the time it takes for the largest visible element on the page to load relative to when the page first started loading. As different elements load, the LCP can change. The browser stops measuring LCP when the user begins interacting with the page, since interactions typically change what is visible to the user. A fast load speed can reassure the user that the page is useful because they are able to quickly begin viewing content.

Elements that can be the LCP:

<img>
<image> inside an <svg>
<video>
Element with a background image loaded using the url() function instead of a CSS gradient
Block-level elements that contain text nodes or other inline-level text elements children

Note

As Google expands their Core Web Vitals, they have indicated <svg> and <video> might be included as elements used to measure LCP in the future.

INP

INP refers to how the page responds to specific user interactions that are programmed into the overall INP metric measured by Google Chrome’s lab data and field data. INP is designed to provide a representation of the overall interaction delay of a page. It does this by working from a sample of the single longest interactions that happen when a user visits the page. For example, if a page has less than 50 total interactions, INP takes into consideration the interaction that has the absolute worst delay. The measurement of INP is a representation of how long a user has to wait in order to interact with the entire page. This is a direct contrast to FID (First Input Delay).

INP is concerned with the following types of interactions:

Any mouse click of an interactive element.
Any tap of an interactive element on any device that includes a touchscreen.
The press of a key on a physical or onscreen keyboard.

Google’s web.dev documentation explains that a good INP value is around 200 milliseconds or less.

Note

INP will be replacing FID in March 2024. The INP score will not impact CWV until March 2024. However, in preparation for this transition, Google has started to inform site owners when INP issues are detected.

Prior to the announcement from Google, Website Builder had already started addressing this metric. As a result many sites already score well on INP, though we are continuing to optimize it.

We are continuing to learn about INP and identifying the optimal practices for both backend operations and site creators. We will update you on what best practices you can put in place are as we learn more. In the interim, if you receive a notice from Google reporting your site has INP issues, please review your site to ensure it is following the current best practices (for detailed information on best practices, see Optimize Your Site for Core Web Vitals).

Rest assured, Website Builder is actively working on optimizing this score and we are confident we will be ready for the official launch in March 2024. If you have any concerns about your INP score before that time, we recommend consulting with an SEO expert for further assistance.

TTFB

TTFB measures the length of time that it takes for the first byte to be transferred by the server.

TTFB has long been suspected as a driver of significant performance gains, which means that it’s a priority that SEO professionals should be optimizing as part of their SEO process.

How to Measure Core Web Vitals

When measuring Core Web Vitals you can use lab or field data. Lab data is gathered from tools that simulate a page load and interaction. Field data is gathered from real user’s interaction with your website. We recommend that you use real-world metrics such as Real User Monitoring (RUM) instead of lab tests so that you can optimize your site more accurately. Google’s CRuX data set can be used to measure your website and is a great choice because it is what Google uses to measure Core Web Vitals.

Both CLS and LCP can be measured in the lab or in the field. FID can only be measured in the field because a real user needs to interact with the content. We strongly recommend you test every page on your website.

The following tools can be used to measure Core Web Vitals:

Field Tools

Lab Tools

Note

To learn more about the differences between Lighthouse and Core Web Vitals, see Lighthouse and Core Web Vitals Comparison.

Ideal Scores

For a page on your website to be considered passing it needs to achieve all the following metrics at the 75th percentile:

CLS. 0.1 layout shift score or less
FID. 0.1 seconds or less
LCP. 2.5 seconds or less

Currently, only 20% of websites pass all three metrics. To learn how to optimize your website, see Optimize Your Site for Core Web Vitals.