**Important:** This feature is available to allowlisted accounts only. Contact your Google representative if you need access to the feature.

<br />

For a given media plan, [`ReachPlanService`](https://developers.google.com/google-ads/api/reference/rpc/v26/ReachPlanService) generates
forecasts of how much it would cost to reach your audience. Media plans are
composed of demographic targeting, campaign duration, device types, and a set of
budgets allocated to various ad formats. The forecast is a curve of reach and
impression levels at increasing budgets.

Subsequent pages in this guide describe how to:

- [Authenticate to the service](https://developers.google.com/google-ads/api/docs/reach-forecasting/authentication)
- [Specify a media plan](https://developers.google.com/google-ads/api/docs/reach-forecasting/media-plan)
- [Generate a curve](https://developers.google.com/google-ads/api/docs/reach-forecasting/generate-curve)

## Glossary of terms

This guide assumes familiarity with [Google Ads](https://ads.google.com), media
planning, and reach curves. The following table explains key terms in detail.

| Term | Definition |
|---|---|
| Census audience size | The census size of an audience for your plan's given country, age range, and gender. |
| Effective frequency | The minimum number of times that a user is exposed to a YouTube ad. |
| Effective CPM | The CPM for on-target impressions. |
| Frequency cap setting | Limits the number of times that a YouTube ad is served to the same user during a specified time interval. The frequency output can sometimes be higher than the frequency cap due to cross-device signals and cookie latency. |
| On-target impressions | Number of ad impressions. This only includes impressions that exactly match the targeting. |
| On-target reach | Number of unique people who may be reached at least the effective frequency number of times. This only includes people who exactly match the targeting. |
| Total impressions | Number of ad impressions. This includes impressions that may fall outside the specified targeting due to insufficient information on signed-in users. |
| Total reach | Number of unique people who may be reached at least the effective frequency number of times. This includes people who may fall outside the targeting. |
| YouTube audience size | The total commercially reachable size of an audience on YouTube for your plan's given country, age range, and gender. |

## What's next

Learn how to [authenticate requests](https://developers.google.com/google-ads/api/docs/reach-forecasting/authentication)
for `ReachPlanService`.