What is Search Impression Share?
Search Impression Share (IS) is the percentage of impressions your search ads receive compared to the total number of impressions they were eligible to receive. If your campaign was eligible for 1,000 impressions but only received 400, your impression share would be 40%.
Google and Microsoft calculate this metric across search networks, helping advertisers understand how often their ads appear when they could appear. It's expressed as a percentage and only accounts for impressions on keywords you're bidding on.
Why It Matters
Impression share reveals whether budget, bid strategy, or ad quality is limiting your visibility. A low IS (say, 20%) might indicate you're losing potential traffic due to:
- Budget constraints – Your daily budget exhausts before day's end
- Low bid amounts – Competitors outbid you for positions
- Ad approval issues – Ads disappear due to policy violations
- Poor Quality Score – Low relevance or landing page experience
For UK agencies managing competitive sectors (finance, retail, travel), improving IS often directly correlates with revenue growth. A 10% increase in IS can significantly boost brand awareness and lead volume.
When to Use It
IS is most valuable when:
- Diagnosing underperformance – High CTR but low conversions might stem from low IS
- Justifying budget increases – Shows impression loss due to insufficient spend
- Competitive analysis – Benchmarking against industry standards
- Campaign optimisation – Identifying whether growth is bottlenecked by reach or conversion rates
Monitor IS monthly and set targets based on business objectives. An e-commerce client might aim for 70%+ IS, while a niche B2B firm might accept 40%.
Impression Share vs Lost IS
Google provides two related metrics:
- Impression Share Lost (Budget) – How often you didn't get an impression because your budget ran out
- Impression Share Lost (Rank) – How often competitors outranked you
These breakdowns help prioritise whether to increase budget or improve bidding strategy.
Limitations
IS doesn't capture intent quality or user engagement. You could have 100% IS on low-intent keywords whilst missing high-intent searches. Always review IS alongside CTR, conversion rate, and ROAS for complete campaign health.
For UK advertisers, IS is particularly useful during peak trading periods (Black Friday, Christmas) when competition intensifies and budgets matter most.