Ad Position Versus Ad Rank

Ad position is not the same as Ad Rank.

Ad position is the order of your ad in the auction results as compared to other ads. For example, an ad position of "1" means an ad was the first ad shown, with no other ads ahead of it. An ad position of "2" was the second ad shown, and so on.

Note that ad position isn’t necessarily the location of your ad on the search results page. For example, an ad position of "1" doesn't necessarily mean that your ad is above the organic search results. It can be your ad position if there are no ads above the search results and your ad is the first ad shown beneath the organic search results. What this means is that you can be in ad position “1” but not qualify to be in any spots above the organic results.

Similarly, an ad position of 2 only means you were the second ad shown by order, and in practice for text ads you could be located in either the second position above the search results, or in the first position below the search results (if the first ad is above the organic search results), or in the second position below the search results (if the first ad is also below the organic search results).

Google Ads calculates Ad Rank for every ad in the auction. Ad Rank determines your ad position and whether your ads are eligible to show at all. Generally speaking, the ad with the highest Ad Rank gets to show in the top position and the ad with the second-highest Ad Rank gets to show in the second position (assuming the ads clear the relevant thresholds), and so on.

Source: https://support.google.com/google-ads/answer/1722122