Definition: The percentage of eligible auctions in which your ad actually appeared. The closest thing in platform data to "how much of the available market am I capturing" — and a direct input to Opportunity Gap thinking.
Formula:
Impression Share = Impressions ÷ Total Eligible Impressions (estimated by Google)
What to look for:
- Lost IS (budget) vs. lost IS (rank): lost to budget means demand exists that you simply aren't funding — often the cheapest growth available. Lost to rank means bids or Quality Score are too low to compete.
- IS on top categories: low impression share on a high-demand category is the paid-search version of an opportunity gap — the market is searching and you're not showing up.
- Absolute top IS indicates how often you hold the premium position on brand-critical terms.
Typical benchmarks: On brand terms, healthy accounts defend 90%+ impression share. On non-brand, anything goes — what matters is whether lost share is budget-constrained (fixable with money) or rank-constrained (fixable with relevance/bids).
What influences it: budget caps, bids and bidding targets, Quality Score, competitor activity, and targeting breadth.
How to improve it:
- Lift budgets on campaigns losing IS to budget and hitting CPA/ROAS targets — this is usually the most defensible growth lever.
- Improve ad rank via relevance and Quality Score where share is lost to rank.
- Defend brand terms aggressively; conquesting competitors there is expensive for them and cheap for you.
Related metrics: CTR, CPC, Quality Score, Opportunity Gap.