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Impression share also known as search impression share (SIS or IS) is the number of impressions you have received divided by the estimated number of impressions you were entitled to receive. Formula for IS:
Impression share = impressions / total eligible impressions
These impression you could have received based on different factors like current ads’ targeting settings, approval statuses, bids, and Quality Scores. Impression share data is available at the campaign, ad group and keyword levels.
Impression share results come in the percentage, for example, a 50% impression share means that out of all the auctions you could have been shown, you were only included in about half of them. It is same like glass-half-empty type situation that means you lost out on 50% of traffic.
To further know about what is Impression share now you understand that impression share is a valuable metric that will allow you to determine areas in your account that need improvement and are eligible to receive more impressions. Considering the optimization seriously, it can help you boost overall traffic and of course site engagement.
100% Search impression share is ideal no doubt but getting this ideal figure is not an easy thing. It depends on your goals, the keywords which you are using, branded keywords and non-branded keywords definitely have their own impression shares. 95% impression share should be considered good in case of branded keywords and in case of non-branded keywords 80% should be the bench mark.
But if your keyword is very competitive and you have a limited budget then you should expect and aiming for search impression share near to 60%. If you are getting less values on search impression share then it is time to optimize and focus on things in your campaign which can help to maximize impression share.
Every click has an opportunity cost. It is possible for the impression you are getting you might be clicking on something which can further lead to conversion but it is not always true that every impression is converted. So getting higher impression share is also not very good, yes it is true! You have to focus on quality not quantity.
What if you are getting 90% impression share but your goal was to get qualified leads and you get nothing out of it then this 90% is useless. You have to see again what good impression share is as mentioned before. So when focusing and analyzing impression share you have to be skeptic enough if you are getting quality impression which is playing an important role in a customer journey.
If you are not getting good impression share then you can also check why your impression share was lost? Was it lost because of rank or was it lost due to less availably of budget. Search impression share is very closely tightened with budget. You can increase the budget and see the impact on impression share but it is not recommended to increase the budget without looking at the other factors like conversion rate, bids, targeting, quality score and CTR.
If you’ve ever tried to add the percentages before, it’s quite possible you will have encountered a problem, as the combined values don’t add up as expected.
What quite a lot of people don’t realize is that impression share is not additive. You can try adding them, but more often than not, you’ll end up with an impression share more than 100%.
To understand the meaning of “not additive”, please consider the following example: In one survey, 80% of the people surveyed said their favorite fruit was bananas. In a different survey, 60% of the people surveyed said their favorite fruit was bananas. We cannot add 80% and 60% to arrive at the conclusion that bananas are liked by 140% of the people surveyed. The values 80% and 60% are not additive.
You might think it’s a glitch in the data, but this isn’t the case.
Let’s find out what is really going on.
Let’s take a look at the following impression share percentages for Match Type.
| Match Type | Impression Share |
| Exact Match | 40% |
| Phrase | 30% |
| Modified Broad | 20% |
| Broad | 14% |
When you add these values together the result is 104%, which may seem like an error.
But here’s the thing:
You aren’t supposed to add these values.
The reason for this phenomenon is simple. Although the “exact”, “phrase”, “modified broad” and “broad” are attributes of the “keyword match type” dimension, they are calculated independent of each other.
Each value isn’t calculated as a percentage of the total impression share. Instead, each one of the match type values is a percentage of the total possible impressions for that specific match type.
Let’s dig a little deeper.
So, let’s imagine a user starts a search on Google. S/he enters a search term that matches with one of your chosen keywords in your ad campaign. As it happens, it’s an exact match.
Whenever this happens, your exact match keyword will be entered into Google Ads keyword auction, where it will be up against your competitors’ keywords.
This time around, you win in the auction, and so your ad receives an impression. Your impression share will increase, and the percentage will depend on the total impressions the keyword can receive as an exact match keyword.
For this example, let’s say the total possible impressions limit is set at 20,000. So, your one new impression would be calculated as follows:
Impression share = (1/20,000) * 100 = 0.005%
Every single time you win an auction for an exact match on this keyword, your impression share will grow. Therefore, in the end, if you win 50% of all the auctions you are entered into, the impression share will be 50% for exact match.
Applying the same concept to the other match types, you must look at the percentage against the total possible impressions of that match type.
If phrase match type has 200 possible impressions, and you earn 60, the impression share will be 30%. Take a look at the table below to understand this.
| Match Type | Impression Share |
| Exact Match | 40 impressions received out of 100 = 40% |
| Phrase | 60 impressions received out of 200 = 30% |
| Modified Broad | 10 impressions received out of 50 = 20% |
| Broad | 21 impressions received out of 150 = 14% |
To clarify, impression share is not additive because the values are based on individual auctions and match types.
Each match type has a separate auction and unique figures for the total impressions of that respective match type. Whenever users enter search queries, the keyword is placed in the respective auction for its match type.
Another scenario to know about is impression share by device type. As the device type is a factor that influences where your keyword is placed in Google Ads keyword auctions, this is another important consideration for marketers.
Similar to the example we explored above, in this case, Google will also have a calculated value for the total impressions each keyword can have depending on each device type.
For example, the keyword “shoes” may have 100,000 total impressions. Out of that total:
When you look at impression share by device type, it’s important to realize that each separate value is 100% of the impression share for that device. So, 40,000 impressions for mobile devices is 100% of the impression share of mobile devices, and 20,000 impressions for tablets is 100% of the impression share for tablets etc.
If a user enters a search term that contains the word “shoes”, which matches a chosen keyword on mobile, your chosen keyword will be entered to an auction just as before.
If you win the auction, the calculation is the same as the one for match types:
Impression share = 1/40,000*100= 0.0025%
If you are fortunate enough to win every auction for mobile devices, the impression share will be 100%. The same goes for the other device types, so you can understand why we shouldn’t add these values as it will clearly exceed 100% in total.
Understanding analytics and key metric values is an integral part of developing successful advertising campaigns.
With a clear sense of impression share values, you can assess your campaign in more detail. The calculations used on match types and device types allow us to drill deeper to discover what is going on with individual aspects of the Ad campaign.
Once you understand that impression share is not additive, and that it must be calculated independently of the other values, it’s quite straightforward.
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