Does Font Size of the H1 Header-1 Affect Search Engine Optimization SEO?

Having a disagreement with a fellow SEO. Do you think the font size of the h1 will effect Search Engine Optimization (SEO)? Ux perhaps but h1 SEO signal?
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I've never read documentation from Google or other that the font size of an H1 is a rank signal.
I have seen H1 tags with smaller font size than H2 and H3 tags, but they still get the priority because of HTML hierarchy. But if the font size is too small for the mobile usability test, that's a different issue which could affect ranking.
"Font size in itself is not a ranking factor, but selecting the right font size contributes to a better user experience. This in turn helps improve the Search Engine Optimization (SEO)performance and the conversion of your website.
Secondly, select the right font size for different headings and subheadings to make the structure of a text clear to search engines and to your users."
It would only affect SEO if it was done to intentionally hide the text. If it's done to make the text look better to users or for design, but the text is still easily read, then no. SEs don't care how pretty or ugly your site is, they just want to give users what they're looking for.
No, but if the font size is too small to read and other competitors have relevant content with mobile-friendly font size, your ranking might be impacted. H1, H2.. the clear heading tags structure is much more important to SEO performance.


Ammon 🎓
It can, yes. But not in a good way. And we've been told this by Matt Cutts, Gary Illyes, and John Mueller, all in their various times saying that when an element is made prominent in some fashion that rendering can detect and recognize, whether that is in a H1 tag, or made bold, or with emphasis, or simply larger fonts, it is all treated in much the same way as a H tag is – a sign that this text is supposed to stand out and is more important.
The corollary to this is that if text in a H1 is made to look 'normal' through Cascading Style Sheets (CSS) or other means, it may NOT be treated as important.
Hard to believe the idiocy these days as it may be, there was a time where some SEO users, on hearing that H tags were rewarded, tried wrapping up entire paragraphs in H1 tags styled to appear to viewers as regular text. Needless to say, it didn't work, and more, was a strong signal of spam.

On a site I am working on we made the largest text at the top of landing pages <p> because it was more for snappy copy. Directly below that was the smaller H1 which was descriptive of the service the landing page was focused on and included the keyword. It was still a heading and larger than H2 etc. in the body of the text. There is no obvious issue ranking for the terms the H1 targeted despite the larger <p> tag line above it.
Ammon 🎓 » John
Yeah, the fact it was a H1 tag, followed by a H2, and otherwise displayed as expected, likely means that Google correctly identified the large P content above the H1 as a stylistic element, much like a logo would be.
Google do still pay attention to Information Architecture, and the use of tags to give structure within the DOM.
I haven't run any recent experiments on this, but my guess is that if you'd styled or sized the H1 down to regular paragraph/body text size, that it still would have just preferred the H2 to that simply larger P text block, but would have placed far, far less emphasis on the H1, probably about equal to mere bolding, or merely resized P text alone as a 'highlight' or spot-lit element.
Truslow 🎓
I've done a few experiments on this recently, but not enough to be absolutely certain about any of this. And some aren't specifically about headings. That said… here are some areas where I feel there is enough correlation in results to be able to say, "It MIGHT be something – and if not, there's enough here to suggest it's probably worth the time to take it into account."
First – and this sort of goes against the rest of the stuff… If you do something incorrectly with absolute consistency, then Google can spot that pattern and adapt.
So… for example, you have no H1's on your page, or maybe every page has your logo and it's alt text as the H1 so it's not technically even visible (as a heading, anyway) and then all your page titles start with the H2 tag instead… it's not technically correct. (Home Page where the "Brand/Site Name" is the most important aspect is the one place where this is typically done and accepted.) So now… your H2s are playing the role of what most sites would use an H1 for.
— With Consistency (i.e. you do that the same way across the site): Google seems to (eventually) figure this out and give your h2's the weight they would normally give an h1.
— Without Consistency (i.e. you do that sometimes, but other times it's just random or doesn't follow the pattern): Google will TRY to get it right and, sometimes, it will succeed – and other times it will fail. You can't control that – so the successes will work out for you, the failures will either hurt your ability to rank for what you want or sometimes even get you ranking for things that aren't really going to convert properly.
As a general rule of thumb – when I analyze a site and I see something not following the proper standards I tend to give it a fairly high priority on my Things to Fix list. BUT… if I see that that thing is being done consistently and it creates a pattern that can leverage into a signal – I tend to lower the priority a bit. Yeah – it still wants to get fixed, but I'm going to push that back a month and get these major issues handled first.
Now – as far as font sizes – in headings or otherwise – I have never noticed, heard about, nor read about anything tangible that happens there. Well… that's not true – as Ammon, Chris, and maybe a few others pointed out – if anything size 0, that can hurt, and if it's anything below 16px, it will hurt your mobile score (which has a small effect on things) because of the "text too small to read" issue.
But – as Ammon pointed out – there is the "relative" factor. It's not any specific font size or anything like that – that which is designed to stand out must, therefore, have a reason for wanting to stand out.
It appears that Google MIGHT even be reading class names and giving them some specific meaning – but I'm not sure here. Here's the story/experiment – one I started purely by accident.
For years, we've been training folks to have a good title for the H1 and then to immediately follow that up with a lede. (Lede is an old newspaper term meaning a quick summary like maybe a paragraph or bullet points that explain what the whole of the article is going to be about). This, by its very nature, helps support the h1 and gives it some meaning – especially if we can get some good semantic triples into the lede.
Now, we also close each post with a summary, a "here's what you've learned" type statement along with the obligatory, "Now contact us and we'll help you solve this issue that you now better understand" or whatever. Basically, it's a "You have the problem, you've learned about <this> solution and <brand> can take care of that for you. Call me!"
During a redesign a few years back, the designer latched onto the whole "every page has a lede" thing and had it so they had a box and background and stood out from the page. So, I just created a css style called "tagline" so they could wrap that first opening section in a div and call it a day. (In a subsequent redesign, I created a custom field because we had people with ZERO html background adding content – so with the custom field for that section, I could have the system automatically wrap it).
Interestingly enough – the standard ledes we'd always done worked well. But I saw with this project that suddenly those ones wrapped in a special div tended to generate rich snippets a lot more frequently and quickly. It's too close to call as to whether it had much, if any, effect on organic ranking, though.
THEN… in another project, it was a site that had no closing Call to Action (CTA)s nor Ledes anywhere. We didn't do a redesign, but went in and created unique ledes and closers for each page. Now, the closers had always been there, and by nature, they always wanted to stand out – so they always had a special div around them in our past work. Here, though, we wanted both the lede and closer to look the same in terms of styling, I just created ONE single class that styled them both. (The idea was to make it so the folks adding the new content didn't need to learn and remember two new class names – and make sure they put them in the right place. Just take both sections and wrap them in the same "tagline" class div.)
What's interesting here is Google seemed to pick up on this and started to make some pretty interesting and fun connections. The Lede describes the page and what it's going to teach you and summarizes everything. The Closer Box does something similar but adds in the key point that makes that final connection between the brand and the situation we're talking about. Keep in mind these are just "divs" too – not a special semantic element or anything – just two divs on the page with the same class that serve the exact same function across the entire site.
With this site, Google not only did the things with rich snippets and our ledes, but it started to make branded connections to the concepts – something it had never really done (with any regularity or without taking specific efforts to try to make that connection happen). Google starts answering questions like "Who can help me with <such and so>?" and instead of giving the answer from the lede, it's creating something (usually an enhanced listing more so than a rich snippet in this case) it's showing that page and the "<such and so> is a problem that includes <page's purpose>.<brand> can help you with that." from the Closer, not the lede.
So, even though the content strategy itself remained consistent – that "one class for two sections of the page that look the same and are logically connected in spite of physical distance" thing really made some changes for us. I've done it on two more sites and have another rebuild in the works that's going to leverage it. They all have had at least SOME success in generating rich snippets this way. And they've all had GOOD success in the single "make the lede standout" thing I described above.
So yeah, for my closer block on this post, I'd say "Styling Matters" – but it's not a specific thing – it's a "relative to the rest" and it seems to also have contextual and consistency value. If you just slap an h2 in there ahead of the h1 because you want the style there and it's not done consistently then it won't mean much. Anything that is a "signal" needs to come from a "pattern." Google's guidelines give us suggestions on best practices to create those patterns which helps ensure that the patterns exist for Google to pick up on and leverage. But you can, at least to some extent, create your own patterns and Google can pick up on those too.


I have no idea, but I stopped thinking about such stuff a long time ago – I simply do things the right way and concentrate on what I know for sure it matters. but I have a story about Google and font size – probably unrelated to your question: I have a website on which my AdSense performance was really poor – low Click Through Rate (CTR) and very low Cost Per Click (CPC). one guy told me "your font is too small, and you simply don't get ads targeted to the proper audience, young people with good eye-vision don't buy products on your niche". I doubled the font size and in a matter of weeks my revenue grew 4 or 5 times.
This is probably where the debate began: "[Section] 2.3 Other Features
Aside from PageRank and the use of anchor text, Google has several other features. First, it has location information for all hits and so it makes extensive use of proximity in search. Second, Google keeps track of some visual presentation details such as font size of words. Words in a larger or bolder font are weighted higher than other words. Third, full raw HTML of pages is available in a repository."
Also, in section 4.1:
"In Google, the web crawling (downloading of web pages) is done by several distributed crawlers. There is a URLserver that sends lists of URLs to be fetched to the crawlers. The web pages that are fetched are then sent to the storeserver. The storeserver then compresses and stores the web pages into a repository. Every web page has an associated ID number called a docID which is assigned whenever a new URL is parsed out of a web page. The indexing function is performed by the indexer and the sorter. The indexer performs a number of functions. It reads the repository, uncompresses the documents, and parses them. Each document is converted into a set of word occurrences called hits. The hits record the word, position in document, an approximation of font size, and capitalization. The indexer distributes these hits into a set of 'barrels', creating a partially sorted forward index. The indexer performs another important function. It parses out all the links in every web page and stores important information about them in an anchors file. This file contains enough information to determine where each link points from and to, and the text of the link."
These quotes are from the 1998 paper "The Anatomy of a Large-Scale Hypertextual Web Search Engine". That paper described a search engine that no longer existed by the end of 2001. Amit Singhal completely rewrote Google after he was hired. But subsequent algorithms looked at text size and prominence.
It would be prudent to assume that Google's use of Feature Learning algorithms allows for a more nuanced weighting of font sizing and decoration than whatever they used 20 years ago. I doubt there's a one-size-fits-all approach to how these things are handled.
The Anatomy of a Search Engine

Ammon 🎓 » Micha
I agree that one has to assume they could, and even that they probably tried more nuanced weighting. But the bigger question, of course, is did more granularity provide better results?
It's been years since I tested this specifically, but back when I did I could find no conclusive evidence to suggest much granularity or gradation of the types of 'prominent' markup. H1 always seemed a bit stronger to me, but honestly just a large bold font for a short first line didn't rank much differently.
If Google differentiate, it has always felt to be only in tiny percentiles of weight.


Doesn’t Google implement anything in SEO that wasn’t mentioned in the Patent?

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