Airtable fields can be tricky to figure out, especially when you want to use those fields in a formula. And lookup fields? Those are the most confusing because the return type isn't always intuitive.
That's why I created this reference table. It lists the data type returned by all field types, including what you'll get from a lookup field targeting each type.
As Airtable adds/changes fields, this table will be updated, so I recommend bookmarking it for quick reference.