How do I pronounce “PER”?

The more common pronunciation used in financial contexts is (pee-ee ratio) /ˌpiː iː ˈreɪʃiːəʊ/ also often written P/E ratio:

• The price-earnings ratio (P/E Ratio) is the ratio for valuing a company that measures its current share price relative to its per-share earnings.

(www.investopedia.com)

You can hear its usage and pronunciation in the following video P/E Ratio

The history of price to earnings ratio:

• “The P/E ratio is today the most commonly used valuation metric in the world.” --- Prof. Janette Rutterford, Open University. The P/E has a long history, but it has not always been the most popular way to value shares. Since the invention of stock markets up until less than 100 years ago, the dividend yield (DY) was the main figure every investor was interested in. The asset backing behind a company was also important. The P/E is, compared to those two, a relatively recent invention. Even the phrase ‘price earnings ratio’ only became popular in the 1920s in the US. In the UK dividends were still what mattered up until the mid-1960s.

(www.moneycontrol.com)