What is Impression Share?
Impression Share (IS) is a key performance metric that measures the percentage of available impressions your ads actually received. If 100 impressions were available in your target audience and your ads received 40 of them, your impression share would be 40%.
The metric is calculated as:
Impressions Received ÷ Estimated Total Impressions Available × 100 = Impression Share %
Why Impression Share Matters
Impression share reveals whether your ads are reaching enough potential customers. A low impression share suggests you're losing visibility to competitors or being limited by budget, bid amounts, or targeting restrictions.
In the UK market, where competition varies significantly by sector and region, impression share helps agencies identify growth opportunities. For instance, a 20% impression share in a competitive sector like financial services or e-commerce indicates substantial untapped reach.
Where It's Used
Impression share is primarily available in:
- Google Ads (Search and Display campaigns)
- Microsoft Advertising
- LinkedIn Ads
- Amazon Advertising
Google also provides lost impression share data, broken into two categories: due to budget constraints and due to low ad rank (quality score and bid issues).
Interpreting Impression Share
Whilst higher impression share is generally preferable, context matters. A 100% impression share isn't always necessary – it depends on your campaign goals and budget efficiency. A B2B agency targeting senior marketing directors in the UK might accept a lower impression share if they're capturing the right audience at acceptable cost-per-acquisition (CPA).
Lower impression share often signals:
- Insufficient daily budget
- Bids too low relative to competition
- Overly restrictive audience or keyword targeting
- Quality score issues affecting ad eligibility
Using Impression Share Strategically
Monitor lost impression share metrics to make data-driven decisions about budget allocation. If you're losing 60% of impressions due to budget, increasing spend may improve ROI if current campaigns are performing well. If losses stem from low ad rank, improving ad quality or increasing bids are more effective solutions.
For multi-channel campaigns across UK regions, compare impression share across different markets to identify where you have competitive advantages or disadvantages.
Impression Share vs. Market Share
Don't confuse impression share with market share. Impression share shows what's available in your targeting parameters; it doesn't reflect actual market dominance or your share of total search volume across all users and devices.