Impression Share is a new Adwords performance metrics which shows the percentage of impressions where your ads were shown out of the total available impressions in the market you were targeting. This new Adwords metrics is similar to “Share of Voice”, a metric more popularly used in the advertising industry which shows the relative portion of ad inventory available to advertisers for a specified time period.

Impression Share metrics is now available for Adwords account holders under the column “Level of Detail” when running an Adwords Account or Campaign Performance report.

Inside AdWords  gives a rundown of what the Impression Share columns represent as follows:

• Impression Share (IS): The percentage of times your ads were shown out of the total available impressions in the market you were targeting. This metric is available at the campaign and account level for search.

• Lost IS (Rank): The percentage of impressions lost due to low Ad Rank (cost-per-click bid x Quality Score).

• Lost IS (Budget): The percentage of impressions lost due to budget constraints.

Impression Share is a good tool to monitor individual ad campaign performance. It gives advertisers better ground on how to effectively carry out their ad campaigns based on competitive trending and rate of being displayed whenever a search related to the ad is conducted.