Frequently used metrics and their recommended values.
First Paint (FP)
First paint indicates the time when the browser depicted the first color on the screen. This refers to a non-default background colour, not to a default background colour. For better understanding, we can consider the first paint as the moment when the browser depicted the first pixel on the screen.
First Contentful Paint (FCP)
First contentful paint indicates the time when the browser renders the first text / image / vector graphic on the screen.
According to the http archive source, processing world data as of 1.4.2020:
- Median desktop: 2.2 s
- Median mobile: 5.7 s
First Meaningful Paint (FMP)
First meaningful paint indicates the time when the browser depicts the content that interests the user. This definition is very vague for mechanical processing, as it depends very much on the specific website. Often in mechanical processing we use FMP as the moment of depicting the biggest change in website layout.
DOM ContentLoaded
The DOMContentLoaded shows the time when the browser loads the complete HTML document and its layout. It doesn’t wait for image styles etc to be loaded.
According to http archive source as of 1.4.2020
- Median desktop: 2.8s
- Median mobile: 7.4s
Onload
Simply put, Onload shows the time when the browser finishes loading.
According to http archive source as of 1.4.2020
- Median desktop: 6.5 s
- Median mobile: 19.6 s
First Input Delay (FID)
First input delay indicates the time from when the user interacts with the page (clicks on a button/link etc.) to when the browser is able to respond to that action.
Time to interactive (TTI)
Time to interactive indicates the time when the page becomes fully interactive. A page is considered fully interactive when:
- The page shows useful content (this is measured by FCP
- Event handlers are applicable to most visible elements
- Page can respond to user interaction within 50 milliseconds
TTI is available for mobile devices only.
According to http archive source as of 1.4.2020
- Median mobile: 9.3 s
Largest Contentful Paint (LCP)
Largest Contentful Paint shows the time when the largest element on the viewer screen (viewport) is visible.
First CPU Idle
First CPU idle measures how long it takes for a page to become basically interactive. A page is considered basically interactive if:
- Not necessarily all, but most elements on the screen are interactive.
- On average, the site can respond to most user actions in a reasonable amount of time.
The definition is somewhat vague. More detailed information
Speed Index
The speed index measures how fast the page content is displayed during the loading process. First, a video recording is created and then the visual progress between frames is calculated. Detailed description
Best practice by Think with Google – under 3 seconds
Time to First Byte (TTFB)
The time before the server starts responding to the sent request (ping). Best practice by Think with Google – within 1.3 seconds.
Request Count (mobile web only)
Number of individual objects that are shown on the mobile site. Best practice according to Think with Google – less than 50
Page Weight Bytes (mobile web only)
Total mobile page size. Best practice according to Think with Google – under 500 kB.
