Lighthouse: Speed Index
Speed Index ( SI ) is a performance system of measurement that measures how quickly your page is visually complete above-the-fold .
SI is subject on the size of the browser opinion port and differs from other metrics like First Contentful Paint ( FCP ) or Largest Contentful paint ( LCP ) because it is not a milestone on your page ‘s load timeline .
rather, it is the consequence of a calculation that reflects your visitor ‘s page experience utilizing a frame-by-frame analysis of your page ‘s load behavior .
SI is very much tied to other page load timings. This makes it a useful overall benchmark for assessing your web site ‘s performance in its entirety.
Reading: Speed Index
How does your site score on this metric?
What does Speed Index measure?
The Speed Index metric unit is a synthetic time that is calculated, not measured. It is computed using ocular differences between frames captured during your page warhead .
Each ocular frame represents fourth dimension intervals, and each captured frame is scored for visual completeness above-the-fold until all content is visible i.e., when the page is visually complete .
The Speed Index measured measures how visually complete your page is by analyzing its load, frame-by-frame .
The individual scores are then added to compute the page ‘s Speed Index. Click here to learn more about how SI is calculated .
Because other metrics like LCP and FCP affect your page ‘s ocular completeness, SI is a capital way to track their impact in the exalted scheme of things.
Read more: What is Kubernetes?
think of Speed Index as a unite metric that accounts for many of the early metrics and audits .
SI, on its own, does not give you much actionable data. however, it represents a practical manner to determine if your page rush optimizations are working .
Speed Index’ effect on your Performance Score
Speed Index accounts for 10% of the total Performance Score .
efficaciously, a lower SI indicates that above-the-fold contented loaded much earlier, giving your visitors the perception of a faster load page .
Thresholds for Speed Index
Flickroom displays the calculate Speed Index in seconds, with a lower time representing a faster load web page .
SI thresholds are, as follows :
- Good – nothing to do here = SI of 1311 milliseconds or less.
- OK, but consider improvement = SI between 1311 and 1711 milliseconds.
- Longer than recommended = SI between 1711 and 2300 milliseconds.
- Much longer than recommended = SI higher than 2300 milliseconds.
How to improve Speed Index?
Note that the particular audits mentioned below likely contribute the most to your SI ; however, your foliate ‘s Speed Index may besides be affected by other optimizations that are n’t mentioned hera.
In general, most operation optimizations that result in a debauched First Contentful Paint and Largest Contentful Paint are besides likely to result in a faster Speed Index for your foliate .
Freeing the main-thread for longer, in particular, ensures that the browser can load all visible content faster for your page visitors ( i.e., faster ocular completeness ). Some of the optimizations hera include :
note : Some of the Structure audits are related ; improving one is probable to improve the others .