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The 3 Quality Score Formulas
Every Advertiser Should Know.

Every few years, we make discoveries about how Google ads works from the inside. Some things they regret revealing, others we figure out by ourselves. In every case, we learn how to better use Google ads to our advantage.

The Cost-Per-Click (CPC) formula.

Cost-per-click formula
CPC is an inversely proportional equation.

In 2009, Google revealed the exact formula that goes into the calculation of how much an advertisers is charged for a click:

Cost-per-click formula

It's an inversely proportional math equation, where the cost-per-click (CPC) is equal to an unknown number that is divided by your known Quality Score. Everytime your Quality Score increases, your CPC decreases.

Cost-per-click formula
CPC at each Quality Score in theory.

Google has since then made changes to this formula, without divulging everything that now goes into it.

They have, hovewer, let advertisers know that the formula now includes an evaluation of Ad Extensions, even though in practice, Ad Extensions haven't proven to be of significant influence.

In practice: When you increase Quality Score, you get added to more ad auctions automatically. Your ad is shown to more people, and in those new auctions, your competitors' bids might be higher, in which case you might not see an immediate decrease in CPC. In those cases, consider reducing your bids when you're using manual bidding, but if you're happy with the additional volume, keep them as is. If you're using an automated bidding strategy, you're good.

The AdRank formula.

AdRank Graph
AdRank is directly proportional to bids and Quality Score.

Ad Rank is a number that determines the position of an ad in the auction. A higher Ad Rank means an ad will show up higher in the search results.

The ad with the highest AdRank gets the #1 position, and the ad with the lowest AdRank gets the last postition, or doesn't show up at all.

The actual number is not directly available to advertisers, but understanding it is crucial to advertising on Google.

AdRank is directly proportional to an advertiser's bids and Quality Score. Quality Score plays an important role into how AdRank is calculated.

AdRank formula

The only two ways of improving AdRank are to increase bids (MaxCPC), or to increase Quality Score.

This graph shows how AdRank increases when you bid from $0.50, to $1.50.

Improving AdRank by increasing bids
Improving AdRank by increasing bids.

This graph shows how AdRank increases with Quality Score.

Improving AdRank by increasing Quality Score
Improving AdRank by increasing Quality Score.

Naturally, advertisers usually opt to improve Quality Score as a cost reduction mecanism that also improves visibility.

In practice: When you get a better AdRank, your ad automatically gets more attention in the form of more clicks to your ads. If the increase comes from higher bids, those new clicks will be more expensive to buy.

The reverse engineered factors formula.

In 2016, our friends at Adalysis reverse ingineered the exact theoritical weight that each Quality Score component holds.

As you know, there are 3 factors of Quality Score that Google gives access to along with the 1 to 10 scale:

  • Expected CTR
  • Ad Relevance
  • Landing Page Experience

For each of these factors, Google attributes one of three qualificators:

  • Above Average
  • Average
  • Below Average

Brad Geddes and his team analysed their data to discover the actual weights of each factor, and uncovered a "point" system equivalent to "Above Average", "Average" and "Below Average", as follows:

Reverse Engineered Quality Score
Reverse Engineered Quality Score Factors. Source ↗

And the corresponding equation that tranlates it into the visible Quality Score:

Quality Score Factors Equation
Quality Score Factors Equation. Source ↗
In practice: What Google says about Quality Score factors is unreliable. You'll often find that increasing Expected CTR also gives better Ad Relevance and even improves Landing Page Experience.

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