If you’re considering a Display Network campaign and want to estimate the reach of different targeting options, you’d use:
- Keyword Planner
- Google Analytics
- Ad Preview and Diagnosis
- Display Planner
Explanation: Display Planner shows you the potential reach and cost of targeting ideas to help you plan your Display Network campaigns. The forecasts can help you understand how your ad groups could perform and historical costs can guide you to the ideas that are within your budget.
Read more here: https://support.google.com/adwords/answer/3056115