How to use the ad impression share calculator
Impression share (IS) is the portion of the impressions your ad was eligible to receive that it actually won. The formula is impressions won ÷ eligible impressions × 100. Eligible impressions are the auctions your ad qualified for based on targeting, keywords and bid settings, which is the same definition ad platforms use in their impression share reports.
Impression share is not the same thing as share of voice (SoV). SoV divides your impressions by the total impressions in the result set, so competitors sit in the denominator. IS puts your own missed opportunities in the denominator instead, so the two numbers can legitimately differ for one campaign.
If you split lost impressions into budget-driven and rank-driven losses, the table shows the share for each cause. A large budget share points to raising the daily budget first; a large rank share points to bids and ad quality. Leave both optional fields blank and the table simply reports total lost impressions as one line.
Frequently asked questions
Not by itself. Pushing share higher usually means raising budget or bids, which can lower efficiency. Check whether the loss came from budget or from rank before deciding.
Most ad platforms do not report the raw number. If you know your reported impression share and actual impressions, divide impressions by the share to back into the eligible figure.