There's also a way to build custom calculations in Looker. For the most part, they're built the same way you'd build formulas/calculations in a Spreadsheet tool like Google Sheets.

For example, if we built a report containing User ID and Payment Amount from the Getting Started: Payments dataset:

We could then use the "Calculations" feature in Looker to build a SUM of the Payment Amount field. After clicking "Calculations" we'd setup our formula like so:

We've labeled our custom calculation "Total Payment Amount", we're formatting it to USD with two decimal places, and our formula is going to compute the **SUM** of the field payment_amount. When we hit "Save Table Calculations" we get the following result:

And if we wanted to also see the **AVERAGE** payment amount we could setup yet another custom calculation in Looker. Looker uses the mean function to calculate the arithmetic average: