The Complete Guide to LSI Keywords

Think you know pretty much everything about on-page search engine optimization (SEO) techniques? There are many resources available to teach you how to improve your on-page optimization, but most of them tend to miss an important and lesser-known concept called Latent Semantic Indexing (LSI). If you haven’t heard of LSI keywords—or don’t know much about them—The Complete Guide to LSI Keywords will help you improve your knowledge. Before you know, LSI keywords will be an integral part of your SEO strategy.

A short note before we dive in. This article won’t discuss topics like off-page SEO, link building or even keyword research. Instead, it is dedicated entirely to LSI keywords. You will learn how to improve your Google rankings by using LSI the correct way.

Let’s dive right in.

Keyword Density: The Predecessor of LSI Keywords

Simply put, keyword density shows the number of times a word appears in your text. It is measured as a percentage. To calculate this percentage, we take the number of times a term occurs on a web page and divide it by the total word count of that page. The bigger the percentage, the higher your chances of ranking better in Google for your selected keywords.

At least that is how it used to be before Panda and Hummingbird. Those were simpler times.

Back in the day, keyword density was the ONLY way in which Google could determine if a particular web page might be relevant. Needless to say, people started taking advantage of this metric pretty quickly. That’s how keyword stuffing was invented.

Image: SEO Ideas
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Keyword Stuffing: The Dark Ages Before Google Panda

Keyword stuffing is the process of littering a web page with a specific keyword in order to trick a search engine into ranking the page ranking higher than it otherwise might.

Makes perfect sense, right?

And it worked for years. To boost your site rank, all you had to do was include your main keyword in your page titles, META descriptions, META keywords, and overuse it in your content. You could literally bump your ranking up significantly (often in the top three results for your keyword) just by increasing your keyword density by 10-15%.

But, that approach doesn’t work any longer. In order to provide better, more relevant search results, Google developed a better way to evaluate web pages for relevancy. This process began with the launch of the Google Panda algorithm in 2011. Search relevancy was improved 2 years later when Google Hummingbird was launched.

Google Panda sought to screen out sites with low-quality, duplicate, or thin content, while Hummingbird was designed to focus on the meaning behind the words—the semantics. With these two important SEO updates, Google prevented useless, low-quality and spammy content from bubbling to the top of search results.

Complete Guide to LSI Keywords Recommendation: Don’t exceed 2-3% keyword density. This way you avoid keyword stuffing problems.

Does Keyword Density Still Matter?

Five years after Google Panda was launched, keyword stuffing is considered an obsolete technique that, when employed, can actually damage your content ranking.

OK, but how does this apply to keyword density? Should we still pay attention to it?

Yes, you should. Here’s why.

Let me give you an example with the term that I’m targeting with this article – LSI keywords.

I analysed the top 10 highest ranking websites for this search query and checked the keyword density of each of them. You can use Free Keyword Density Analyzer Tool from for this purpose.

Here’s a table with the results in terms of keyword density percentage (you can click on the image below to enlarge, download, or print).

Image: Keyword density table, Complete Guide to LSI Keywords
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Keyword density analysis table: LSI keywords

My keyword density analysis yielded the following four very important things:

  1. The most often used keywords (LSI, keyword, keywords, search, SEO, Google and 10 other keywords displayed in the table above) for each of the top 10 highest ranking web pages
  2. The average keyword density (expressed as a percentage) for each keyword on each of the top 10 highest ranking web pages
  3. The number of times each of the keywords are mentioned on the top 10 highest ranking web pages

    “LSI” and “keyword” are present on each of these high-ranking pages. They are the words with the highest correlation level. This means if you wanted a web page you manage to rank for the LSI keywords, you MUST use these terms in your content, too.

  4. The average content length for each of the top 10 highest ranking web pages. The longer the average page content is, the longer the content you should write yourself. Content length does matter—big time!

Complete Guide to LSI Keywords Recommendation: Always perform LSI and keyword density analysis upfront. This way you will know what you’re up against and you’ll be able to design a strategy to outrank your competitors.

From time to time, you will come across sites that have unusually high keyword density levels. For instance, Its keyword density percentage is quite high and is not representative of the average. Use the average percentage of the other 9 web pages as your target instead—somewhere between 0.7 and 2.8% for “LSI.”

When you perform a keyword density analysis on your content, exclude the most irrelevant results from your final list. Remember, SEO is all about finding patterns, analyzing them thoroughly, and obtaining actionable data. Keyword density analysis can provide you with vital insights, including competitive analysis data, enabling you to learn from the successes of others who have adopted on-page SEO best practices. Knowing which keywords your competitors are using—and what their keyword density percentages are—allows you to replicate successful tactics and ensure your content ranks as high as possible.

Complete Guide to LSI Keywords Recommendation: These techniques are most useful when combined with link-building efforts, and high quality, relevant, and useful content.

Image: SEO Idea
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LSI Keywords—The Modern Way of Doing On-Page SEO

LSI stands for Latent Semantic Indexing. It might sound complicated at first reading, but it’s not really. LSI keywords are words or phrases that are semantically related to each other. They are not limited to synonyms or keywords with similar meanings. They are most often keywords that commonly are found together.

Here’s an LSI keywords example. Let’s say that you are writing an article about cars. You could be writing about any one (or more) of these 5 things:

  1. Cars—vehicles
  2. “Cars”—an animated Disney movie
  3. CARS—Canadian Association for Rally Sports
  4. CARs—Canadian Aviation Regulations
  5. The Cars—an American rock band

So how do search engine algorithms know which topic you are writing about?

They do so by leveraging LSI keywords. Basically, the Googlebot scans your page searching for closely related terms which can help it understand your content better.

Let’s go back to our LSI keywords example about cars.

Here are some Latent Semantic Indexing keywords that Google might have found on your pages if you were writing about one of the topics given above.

  1. Cars—vehicles (vehicle, used, new, buy, sell, dealers, repair, etc.)
  2. “Cars”—an animated Disney movie (film, movie, produced by, directed and co-written by, motion picture, Walt Disney, etc.)
  3. CARS—Canadian Association for Rally Sports (association, rally, sport, championship, Canadian, etc.)
  4. CARs—Canadian Aviation Regulations (aviation, regulations, administration, aerial, aerodromes, airports, etc.)
  5. The Cars—an American rock band (rock, band, music, guitar, drums, song, etc.)

There are actually many terms related to Latent Semantic Indexing. Here are a few of them:

  • Latent Semantic Analysis
  • Natural Language Processing
  • Phrase-Based Indexing and Retrieval
  • Term Frequency-Inverse Document Frequency
  • Latent Dirichlet Allocation
  • Probabilistic Latent Semantic Analysis
  • Hidden Topic Markov Model
  • Latent Dirichlet Allocation

Of course, you don’t have to know everything about SEO in order to improve the semantic value of your content. But, if you’d like to dig deeper, here are a few resources to get you started.

  1. Keyword Usage
     A Visual Guide to Keyword Targeting and On-Page SEO
  2. TF-IDF
  3. Synonyms and variants
     Helping computers understand language
    • How Google May Substitute Query Terms with Co-Occurrence
  4. Page Segmentation
     Systems and methods for analyzing boilerplate
     Document page segmentation in optical character recognition
  5. Semantic Distance and Term Relationships
     Google Defines Semantic Closeness as a Ranking Signal
     Document ranking using word relationships
  6. Co-occurrence and Phrase Based Indexing
    Phrase Based Indexing and Semantics
     Ranking Webpages Based upon Relationships Between Words
  7. Entity Salience
     A New Entity Salience Task with Millions of Training Examples
     Teaching machines to read between the lines

Want to dig really deep? Start with this great article from Moz which explains what you need to know in more detail.


Image: SEO Content is King
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How do we find LSI keywords?

There are 4 easy ways to find Latent Semantic Indexing keywords:

  1. Google’s instant search
  2. “Searches related to” results
  3. Bold words in SERP results
  4. Keyword research tools

Finding LSI keywords via Google Instant Predictions

You can identify LSI keywords for your SEO campaign by typing your keyword into Google’s search box and noticing the suggestions it returns for you. Make sure you turn on the Google instant search results feature.

Image: Google Instant Search, Complete Guide to LSI Keywords
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Finding LSI keywords via the “Searches related to” feature

Just type your keyword in the Google search box and scroll down to the bottom of the results page. There you will find 8 additional suggestions you can add to your LSI arsenal. Note that some of them might not be a good fit for your purposes, so make sure they make sense and are useful for your readers. After all, you don’t want to include LSI keywords like fun easy learn English in your article. Instead, you may consider creating a variation like fun and easy way to learn English. Much better!

Image: Related searches results from Google, Complete Guide to LSI Keywords
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Finding LSI keywords via bolded words

When you perform a search, you’ll notice that Google shows certain words in bold black text. These are LSI keywords. Find ways to implement them in your own copy that make sense to readers. They will help ensure your content is more relevant to—and more findable by—others.

Image: Keywords bolded in search results, Complete Guide to LSI Keywords
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Finding LSI keywords with the help of some tools

If you have already exhausted the first 3 methods for finding Latent Semantic Indexing keywords it’s a good idea to enrich your LSI arsenal by using some LSI tools. Begin with the most popular tool, Google AdWords Keyword Planner (Google AdWords account required; how to sign up). Once you’re logged in, type your keyword and click “get ideas.”

You will see two different tabs in this tool which are great sources for LSI keywords: Ad group ideas and Keyword ideas.

  • Ad group ideasThis is one of the best sources for LSI keywords. Just go through the list of keyword suggestions and make sure you include as many as possible in your final copy.

Google AdWords ad group ideas, Complete Guide to LSI Keywords
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  • Keyword ideas—Everyone knows this one but very few of you have actually used it as a way to find LSI keywords. You can start using it today.

Image: Google AdWords keyword ideas, Complete Guide to LSI Keywords
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Other Ways to Locate LSI Keywords

There are a variety of small SEO tools and plugins specifically designed for this purpose.

  • LSIGraph—LSI Keyword Generator—LSIGraph is a very easy to use, but yet a very powerful tool. The LSI Keyword Generator provides you with a long list of potential LSI keywords—and it’s free.

Image: LSI Graph Keyword Generator, Complete Guide to LSI Keywords
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  • SEOPressor plugin—SEOPressor is an on-page SEO plugin for WordPress that helps you do on-page search engine optimization. It’s also pretty simple to use (see step-by-step tutorials). And, it’s affordable. Basic plans start at just $5 USD per month. SEOPressor is powerful because it allows you to perform multiple keyword analysis, over-optimization check, social SEO integration, and structured data support. Finally, you can even do an automatic smart linking to reduce your bounce rate.

Image: SEO Processor, Complete Guide to LSI Keywords
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  • Twin word SEO plugin—Another good WordPress plugin for LSI is Twinword SEO plugin. This is an LSI and long-tail keyword research tool that automatically suggests keywords related to your content while you write it. It provides filterable, sortable data, automated keyword suggestions, and details about keywords including monthly search volume, number of results (to help you select the keyword with the lowest competition), as well as a keyword efficiency index (to help you find the most effective keywords to use) and keyword usage tracking.

There are many other keyword generators that can be used as LSI keyword generators, but here’s a list of my 4 favorites:

Why LSI Keywords Are Not Just Synonyms

As I mentioned earlier in this article, LSI keywords are not exactly synonyms. They are actually closely related and relevant terms.

Here’s an example: Imagine that you want to write an article about pizza and you want to know which terms you have to include in order to stand a better chance to rank high with LSI from on-page point of view.

Run the word “pizza” through Keys4Up first.

Image: Keys4Up Screenshot showing findings for search term "pizza", Complete Guide to LSI Keywords
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Now let’s see what SEMRush related keywords tool holds for us:

Image: SEM Rush Related Keywords, Complete Guide to LSI Keywords
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See the HUGE difference in the results?

We’re no longer seeing a list with keyword ideas based solely on the word we enter in the tool, instead these results give us a different vantage point from which to consider Latent Semantic Indexing keywords.

LSI Keywords in Review

If you’re writing about pizza and you want to make sure you are using LSI to rank as high as possible, make sure to also include terms like: cheese, pepperoni, delivery, crust, food, ingredients and restaurant for best results. As you can see, LSI keywords are not just variations of your main keyword. They are closely related terms which Google likes to see when it crawls pages about a particular keyword.

It’s all about patterns.

How to use LSI keywords in practice?

Now that we already know what LSI keywords are and how we can find them, it’s time to start using them to improve our on-page SEO and organic rankings.

Here are the main areas where you can place LSI keywords to get the most out of them:

  • Page title
  • H1 and H2 tags
  • URL address
  • META tags
  • Images alt text
  • First paragraph of text
  • Body of content
  • Links anchor texts
  • Last paragraph of text

Complete Guide to LSI Keywords Recommendation: Implement LSI keywords after your copy is completed, not before. This allows you to make sure that you write for your audience first and for search engines after-the-fact. And don’t forget the importance of keyword density. It matters.

Now that you’re well-acquainted with the LSI keywords and know how to take advantage of them, get busy. You’ve got content to optimize. What are you waiting for? Get busy!