Impression Share

Impression Share is the percentage of available ad impressions your ads actually received, out of the total number they were eligible to win given your targeting, budget, and bids. If 1,000 auctions matched your settings and your ad showed in 600 of them, your impression share is 60%.

Why it matters#

Impression share answers a question raw impression counts cannot: how much of the available demand am I capturing? A campaign can serve millions of impressions and still leave most of the market untouched. The gap below 100% is usually attributed to two causes: lost share due to budget (you ran out of money) and lost share due to rank (your bid or quality was too low to win the auction). Splitting the gap this way tells you whether to raise budget or improve bids and creative.

How it works#

The metric is most common in Google Ads and other auction-driven platforms, but the concept applies anywhere ads compete for a finite pool of placements, including the Native Ad Auction. Each time a user becomes eligible to see an ad in your category, that counts as one available impression in the denominator; each Ad Impression you actually win adds to the numerator.

Impression share is closely related to Share of Voice (SOV), but they are not identical: share of voice often measures presence across an entire market or competitor set, while impression share is scoped to the auctions you specifically qualified for.

Related terms: Ad Impression, Share of Voice (SOV), and Native Ad Auction.