Definition
Impression share is the % of times your ads were shown out of total eligible impressions (search).
How to use it
- Lost impression share usually comes from budget limits or low rank (bid/quality).
- Increase impression share only if marginal ROAS/profit supports it.
Measured as
Measure Impression Share with a fixed attribution window, conversion event, and spend basis before comparing campaigns or creative tests.
Operator takeaway
- Lost impression share usually comes from budget limits or low rank (bid/quality).
- Increase impression share only if marginal ROAS/profit supports it.
- Use Impression Share only inside a stable attribution rule, conversion definition, and time window so campaign comparisons stay honest.
- If performance changes, check whether the metric moved for a real business reason or because the measurement setup changed underneath you.
Next decision
- Read Marginal ROAS: how to scale ads with diminishing returns if the decision depends on interpretation, policy, or trade-offs beyond the raw formula.
- Decide which report owns Impression Share before comparing campaigns, channels, or creative tests.
Where to use this on MetricKit
Guides
- Marginal ROAS: how to scale ads with diminishing returns: A practical guide to marginal ROAS: why average ROAS misleads at scale, how diminishing returns work, and how to pick a profit-maximizing spend level.
- Attribution vs incrementality: what to trust, when, and how to test: A practical guide to attribution vs incrementality: common attribution models, window pitfalls, how MER/marginal ROAS fit in, and how to run holdout/geo tests.