Impression Share
The share of the impressions you were eligible for that your ads actually won.
Impression share is the percentage of the impressions your ads were eligible for that they actually won: impressions received divided by total eligible impressions. Google also reports what you lost, split into impression share lost to budget and lost to rank.
That split is the useful part. Share lost to budget means you are leaving winnable, profitable traffic on the table and could scale; share lost to rank means your bid or Quality Score is holding you back. On your own brand terms you want impression share high, near 90%, which is the heart of brand defense: not letting competitors skim your cheapest demand.
Read it alongside the rest of the account rather than as a target in itself; high impression share on unprofitable terms is not a win.
Put the number to work: the break-even ROAS calculator turns your margins into the ROAS you need, and a free Due Diligence Audit checks whether the figures you see are the ones you are getting. Back to the glossary.