Sum Formula

Using the Power Apps Sum Formula: Whenever you have a collection or table or gallery of values that you need to sum together, use the Sum function in Power Apps. Here, we’ll take a look at an example where the values are inside a gallery, and we’ll perform a sum formula on that collection of rows. The first parameter is for the table or collection, and the second parameter is the name of the field you want to sum together.

-Darren Neese with PowerApps Tutorial