What Are Google’s Core Web Vitals? What Do They Mean?

This year is a big for site speed.

Sure, site speed has always been important but this year we see the introduction of Core Web Vital metrics from Google, which they say they will be rolling out in May 2021.

This is big news, mostly because Google hardly ever warn us nowadays when big changes are going to be made to the ranking algorithm. So it’s say to that if they are telling us ahead of time, it’s probably a good idea to heed their advice.

What are Core Web Vitals

These break down into three main areas, not all of them are to do with speed but they are all important to note.

LCP (Largest Contentful Paint)

Let’s tackle the one about speed first.

It’s always been said that Google likes fast websites, and the common rules of thumb is that it needed to load within 3 seconds.

The problem is that, it wasn’t clear what “load” meant. We now know that website loads in different stages and a web page can load and be useable whilst some other elements may still be loading that a user can’t see.

So it was always up for debate what this meant. LCP now put this to bed.

LCP marks the time when your website loads the main body of it’s content and essentially becomes usable.

Other things may still be happening in the background and loading it, but LCP is the yardstick Google will be using to measure your site against everybody else, thus we are using the same rulebook.

Well done Google, this was much needed.

Later on we will be taking a look at some of the things you can do to your WordPress site to ensure that your LCP load speed is as fast it can possibly be.

FID (First Input Delay)

This is a secondary site speed metric which can muddy the waters a little bit and can be a little confusing.

Once a site has loaded its content and it becomes readable there can be a delay between this and when a user can actually start engaging with the content that is on the page.

This could be completing a form or playing a video on the page.

This time metric will be monitored by Google and if it takes too long, and we are talking hundredths of a second here, then you will start to see FID issues being flagged.

CLS (Cumulative Layout Shift)

Ignore the complicate names, these just make thing more confusing.

However, CLS is probably something we have all experienced. It’s annoying and Google want to eradicate it.

You are buying a product online, you know you want it, so you are blasting through the basket and checkout process.

You fill out all your details…you hit the next button to review all your order details. You know it’s right so you are waiting for the “Order Now” button to appear… It appears… Quick as a flash you go to hit it…but at the last second the button shifts as something else loads nearby and shunts it off.

By accident you hit the back button and you’ve got to do all this again.

This is CLS it’s the amount of time items keep moving around the page. The higher the number, the more it’s moving and you need to reduce that as much as possible.

How do I test my site?

As these are Google metrics the best tool to use will be Google’s own PageSpeed Insights Testing Tool.

Now, this isn’t the most easy to understand tool, however not many site speed tools are.

You are going to be hit with a lot of numbers and a lot of code jargon.

Here is a little look at this websites home page PageSpeed Insights test results…

Eeekk… Looks like I need to take a look at my own site!

You’ll probably have noticed here that I have no FID metric.

That’s because FID can only be measured by people engaging with the site. Google monitors “in the field” if you have enough traffic to your site to report back to Google and that data will appear here.

Clearly, my website, at the moment, doesn’t have enough traffic running to it to show any “In the Field” data.

Here is a look at BBC’s website results with “In the Field” data…

BBC.co.uk PageSpeed Insight results with “In the Field” data.

As you can see BBC’s in the field data is much better than its lab data. The traffic light bars below each metric define the amount of field data proportioned out.

However, on average, the Core Web Vitals for BBC look pretty strong on their homepage.

Here is my recommendation on reading this data;

  • Ignore the scores out of 100, this is a vanity metric more than anything else.
  • Most websites now are mobile first so attempt to focus on the mobile data.
  • Just focus on the traffic light system of LCP, FID and CLS.
  • If you have green or amber numbers, you are doing okay.
  • If you have red numbers look to optimise.
  • This tools tests page by page not your whole site, so be sure to run your website through a number of different page types, homepage, blog holder and blog page.
  • If you are lucky enough to have large amounts of traffic running to your site use the “In the Field” data as a guide.
  • However, if you are doing ad-hoc optimisation, you’ll only see improvement in your Lab Data.
I know it’s tempting, but simply ignore this score. It’s largely a vanity metric.

If I make no changes, and I run PageSpeed Insights does it change?

The answer to this is usually pretty simple. Your server is not a constant.

Particularly if you are using Shared Hosting, which I know many bloggers will be, then your server will be sharing its resources with many other websites.

Depending on the demand on that server or the other websites, this could mean that your website slows down or speeds up.

If you are concerned about your servers capabilities then you can take a look at your PageSpeed Insights results as a guide…

My warning here to reduce initial server response time can really only be rectified by my hosting provider.

Take a look at the warning here which asks me to “Reduce Initial Server Response Time”.

I can’t optimise this by doing anything on-site, however if you see this then you may wish to open a conversation with your hosting provider.

To help with this, I’m going to move my entire site over to a new hosting provider to see if this speeds things up.

In my next article, I’m going to be taking my site through this very process, both on-site and off-stie to try and speed it up (and cripes does it need it!).