GLOSSARY

The percentage of impressions an advertisement receives compared with the estimated number of impressions it was eligible to receive.

Impression share helps advertisers diagnose limited visibility and distinguish missed reach caused by budget constraints from missed reach caused by auction rank.

A search campaign has 45% impression share and 40% search lost impression share due to budget, prompting a review of budget allocation before bids are increased.

It is an estimated, platform-specific opportunity metric rather than a measure of profitability. A higher share can increase cost without improving conversions, and changes to targeting alter the eligible-impression denominator.

Google Ads calculates impression share as impressions divided by estimated eligible impressions. Eligibility depends on targeting, approval status, bids, quality and other auction conditions; separate metrics report share lost because of budget or rank.