How do you calculate the the number of Contacts for each Account record?
Quickly deploy one of Rollup Helper's pre-built rollups named, "Number of Contacts." The Number of Contacts use case calculates the amount of Contacts for each Account record. This use case deploys one Rollup Helper setting and one field, "rhuc_Number_Of_Contacts."
Once logged into your Salesforce organization click on the App Launcher or All Tabs and search for "Rollup Helper." Click on the "Deploy Pre-Built Rollups" tile and click Deploy next to the Number of Contacts label:
You will also be able to view and edit the deployed rollup via the All Rollups page.