Revenue per impression is useful for assessing the overall efficiency of paid media spend since it includes both clickthrough rate and conversion rate. This measure is not used much compared to Return on Advertising spend (ROAS), but is a useful addition when testing ad effectiveness.
Revenue per impression is recommended by Google Ads specialist Brad Geddes in this article giving this example:
“If we just want the most conversions possible; then ad 3 is our clear winner. It receives 15 conversions for every 10,000 impressions. If our goal is the most conversions – this is our winner. However, it has a lower ROAS and RPI than some other ads.
If our goal is ROAS (Return on Advertising spend); then ad 1 is our winner. It’s also our highest converting ad. However, it has a low CTR and thus is going to have a poorer quality score than some of the other ads. It has a lower RPI and makes less money than some other ads. This is why ROAS is a good metric for bid management, but rarely for ad testing.
If we want the most revenue possible, then ad 4 is our clear winner. It’s the highest revenue and highest RPI (because the impressions are equal among all the ads)”.