This article is written for those who want to get better at using price to earnings ratios (P/E ratios). To keep it practical, we'll show how Waterco Limited's (ASX:WAT) P/E ratio could help you assess the value on offer. Looking at earnings over the last twelve months, Waterco has a P/E ratio of 20.33. That is equivalent to an earnings yield of about 4.9%.

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Check out our latest analysis for Waterco

How Do I Calculate A Price To Earnings Ratio?

The formula for price to earnings is:

Price to Earnings Ratio = Price per Share ÷ Earnings per Share (EPS)

Or for Waterco:

P/E of 20.33 = A$1.6 ÷ A$0.079 (Based on the year to December 2018.)

Is A High P/E Ratio Good?

The higher the P/E ratio, the higher the price tag of a business, relative to its trailing earnings. That isn't a good or a bad thing on its own, but a high P/E means that buyers have a higher opinion of the business's prospects, relative to stocks with a lower P/E.

How Growth Rates Impact P/E Ratios

Earnings growth rates have a big influence on P/E ratios. Earnings growth means that in the future the 'E' will be higher. That means even if the current P/E is high, it will reduce over time if the share price stays flat. So while a stock may look expensive based on past earnings, it could be cheap based on future earnings.

Waterco shrunk earnings per share by 34% over the last year. But over the longer term (5 years) earnings per share have increased by 5.5%.

How Does Waterco's P/E Ratio Compare To Its Peers?

We can get an indication of market expectations by looking at the P/E ratio. You can see in the image below that the average P/E (18.1) for companies in the leisure industry is lower than Waterco's P/E.

Its relatively high P/E ratio indicates that Waterco shareholders think it will perform better than other companies in its industry classification. Shareholders are clearly optimistic, but the future is always uncertain. So investors should always consider the P/E ratio alongside other factors, such as whether company directors have been buying shares.

Don't Forget: The P/E Does Not Account For Debt or Bank Deposits

The 'Price' in P/E reflects the market capitalization of the company. That means it doesn't take debt or cash into account. In theory, a company can lower its future P/E ratio by using cash or debt to invest in growth.

While growth expenditure doesn't always pay off, the point is that it is a good option to have; but one that the P/E ratio ignores.

Is Debt Impacting Waterco's P/E?

Waterco's net debt equates to 29% of its market capitalization. While that's enough to warrant consideration, it doesn't really concern us.

The Verdict On Waterco's P/E Ratio

Waterco trades on a P/E ratio of 20.3, which is above the AU market average of 16.1. With modest debt but no EPS growth in the last year, it's fair to say the P/E implies some optimism about future earnings, from the market.

Investors have an opportunity when market expectations about a stock are wrong. People often underestimate remarkable growth -- so investors can make money when fast growth is not fully appreciated. Although we don't have analyst forecasts, you could get a better understanding of its growth by checking out this more detailed historical graph of earnings, revenue and cash flow.

Of course you might be able to find a better stock than Waterco. So you may wish to see this free collection of other companies that have grown earnings strongly.

We aim to bring you long-term focused research analysis driven by fundamental data. Note that our analysis may not factor in the latest price-sensitive company announcements or qualitative material.

If you spot an error that warrants correction, please contact the editor at editorial-team@simplywallst.com. This article by Simply Wall St is general in nature. It does not constitute a recommendation to buy or sell any stock, and does not take account of your objectives, or your financial situation. Simply Wall St has no position in the stocks mentioned. Thank you for reading.