Show the Sum of Products associated to Opportunities on the Account object

To display the total count of Products on an Account record, complete both steps below in order.

Step 1: Create a COUNT Roll-Up Summary Field on Opportunity

This field counts the number of Products (Opportunity Line Items) on each Opportunity.
In Lightning Experience: Gear Icon | Setup | Object Manager | Opportunity | Fields & Relationships | New
In Salesforce Classic: Setup | Customize | Opportunities | Fields | New

1. Data Type: Roll-Up Summary. Click Next.
2. Enter the Field Label and Field Name. Click Next.
3. Summarized Object: Opportunity Product.
4. Roll-Up Type: COUNT.
5. Filter Criteria: Select "All records should be included in the calculation" (or specify criteria if needed). Click Next.
6. Set field visibility for the necessary profiles. Click Next.
7. Add the new field to the appropriate Page Layouts.
8. Save.

This field now shows the count of Products related to each Opportunity.

Step 2: Create a SUM Roll-Up Summary Field on Account

This field sums the Opportunity-level COUNT field created in Step 1, giving you the total Products across all Opportunities on an Account.
In Lightning Experience: Gear Icon | Setup | Object Manager | Account | Fields & Relationships | New
In Salesforce Classic: Setup | Customize | Accounts | Fields | New

1. Data Type: Roll-Up Summary. Click Next.
2. Enter the Field Label and Field Name. Click Next.
3. Summarized Object: Opportunity.
4. Roll-Up Type: SUM.
5. Field to Aggregate: Select the Roll-Up Summary field created in Step 1 (the COUNT field on Opportunity).
6. Filter Criteria: Select "All records should be included in the calculation" (or specify criteria if needed). Click Next.
7. Set field visibility for the necessary profiles. Click Next.
8. Add the new field to the appropriate Page Layouts.
9. Save.

This field now shows the total number of Products associated with all Opportunities on the Account.