Impression Share
Impression share is the percentage of impressions your ads received divided by the total impressions they were eligible for. Google also reports lost impression share due to budget and due to rank, showing why you missed the rest. It reveals how much of your available market you are actually capturing.
Why It Matters
Impression share shows your headroom for growth. If you are winning only a fraction of eligible impressions, you know whether budget or ad rank is holding you back and where to invest to capture more demand.
Common Mistake
Chasing 100 percent impression share as a goal. Dominating every auction is usually expensive and inefficient. The last slices of impression share often come at a steep cost per acquisition.