Determine how many impressions to book

The number of impressions you can book for a prospective line item depends on how willing you are to displace or preempt existing inventory.

First, run a forecast for the prospective line item. Remember that your line item's trafficking criteria can greatly affect the number of available impressions.

Results on the first page of the forecast provide guidance that can help you decide how many impressions to book. You can also gauge and adjust the effect that booking the prospective line item would have on existing line items by viewing contending line items.

How forecasting accounts for trafficking criteria

Forecasting takes most trafficking criteria into account when determining available inventory, but it's good to be aware of the following details.

Consideration Details
Frequency capping Frequency capping is considered, but monthly or lifetime frequency caps are not captured as part of the data. Consequently, in cases with monthly and lifetime frequency caps, forecasting can overpredict availability.
Priority Forecasting looks at priority to determine the Reserved by lower-priority line items number--the number of impressions a line item can get if you’re willing to take impressions from same- or lower-priority line items. Priority is also taken into account when calculating Impressions likely to deliver..
Deliver impressions (evenly, frontloaded...) Ad Manager simulates all line items as evenly paced, regardless of their actual “Deliver impressions” setting.
Cost While cost is not a criteria considered in forecasts, you can view the revenue impact of contending line items.
Roadblock ads

When you run a forecast on roadblock ads, Google Ad Manager records which impressions occurred together when a page is viewed--this is called page awareness. And forecasting takes into account the type of roadblock you're interested in booking, those set up to work with all of the creatives in the line item, or those that work with master/companion creative sets.

For example, a line item containing one creative that’s 728x90 and one that’s 300x250 has these forecasted page views in the following distribution:

  • Page A: the 728x90 creative serves 2 times without the 300x250.
  • Page B: the 300x250 creative serves 1 time without the 728x90.
  • Page C: both creatives serve together (the roadblock) 4 times.

In this scenario, the forecasting model lets you know that 4 roadblock impressions are available, because it's aware that only Page C can serve the roadblock with both creatives.

Multiple creatives of the same size

If you have an ad with multiple creatives of the same size and you select the As many as possible or One or more setting for displaying creatives, you must click Provide some creative details to enter the number of creatives for each size.

Adding creative sizes and counts allows for better forecasting. If you don't include a creative count for each inventory size, forecasting will assume one creative per size. For example, if you have an ad that has two 300x250 creatives, and a webpage with two ad slots of that size, the forecast model counts one page view as one impression, whereas in reality, both creatives will serve, making two impressions.

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