If your ads were eligible to appear 10,000 times and showed 6,000 times, your impression share is 60%. Google breaks the missing share into two causes: impression share lost to budget (your budget ran out) and lost to rank (your Ad Rank was too low). Related metrics show how often you appeared at the top of the page or in the absolute top position.
Impression share is a powerful planning tool. High share lost to budget on a profitable campaign is a clear signal to invest more; high share lost to rank points to bids, ad quality, or landing pages. For branded campaigns, an impression share near 100% is usually the goal.
Example
A campaign shows 55% search impression share with 35% lost to budget — evidence that more spend could capture more existing demand at a similar cost.
How Sloss Digital uses it
We use impression share to find room to scale profitable campaigns and to tell whether the fix is more budget or better quality.