Spend long enough in investing circles, and you'll hear the term "multiple" tossed around. Wondering what it means? Here's a quick primer.

"Multiple" basically refers to a number that compares one of a company's vital statistics to another. The most common example is the price-to-earnings (P/E) ratio, frequently referred to as the "earnings multiple."

Let's use Amgen (NASDAQ:AMGN) to illustrate. It was recently trading for around \$63 per share, and its trailing 12-month earnings per share (EPS) was \$3.88, excluding extraordinary items. Divide \$63 by \$3.88, and you'll get a P/E ratio of 16.2. You could also say that Amgen's recent price was 16.2 times its EPS, or that it's trading at a multiple of 16.2. Got it?

Multiple multiples
The P/E is just one of many multiples. The price-to-sales (P/S) ratio, in which you divide a company's market capitalization by its trailing 12-month revenue, is useful for evaluating companies that aren't yet profitable. There's also a price-to-book value multiple, a price-to-cash flow multiple, and so on.

You can find particularly promising companies by searching for low multiples and solid expected growth rates for EPS. That can give you a one-two punch: The low multiple will presumably catch up with itself, which it can only do if the stock price rises or EPS shrinks. And growing EPS can also fuel stock-price appreciation.

Imagine Meteorite Insurance (Ticker: HEDSUP), trading at \$20 per share with EPS of \$2 per share. Its P/E would be 10 (20 divided by 2). As earnings grow, its stock price will likely follow suit. So when EPS hits \$4, if the P/E ratio has held steady, the stock might be in the \$40 range. Now imagine that the P/E has risen closer to its historic mean, or to its industry range, becoming 15. Given an EPS of \$4, that would imply a stock price in the neighborhood of \$60.

Screening for multiples
Multiples can also help you screen for promising stocks. Here are some of the ideas I found when searching for large-cap companies with price-to-cash flow (P/CF) ratios below their industry average, and hefty net margins that have risen over the past three years.

Company

CAPS Rating (Out of 5)

P/CF Ratio

Industry P/CF Ratio

Net Profit Margin

Amgen

****

12.5

23.8

30.1%

Xilinx

***

13.6

31.8

20.6%

EnCana (NYSE:ECA)

*****

3.9

5.4

22.6%

Newmont Mining (NYSE:NEM)

***

12.0

17.8

14.7%

First Solar (NASDAQ:FSLR)

**

26.1

31.8

31.8%

Apollo Group (NASDAQ:APOL)

**

12.9

17.1

19.7%

*****

4.0

22.0

18.3%

Medtronic (NYSE:MDT)

****

13.5

17.9

14.9%

Data: MSN Money, Motley Fool CAPS.

Note two caveats, though. First, these ratios don't reflect free cash flow -- a metric that takes into account money spent on capital expenditures. Also, not all of these stocks are equally well-regarded by our Motley Fool CAPS community of investors. In short, don't take this as an automatic buy list -- just a starting point for your own further research.

Don't multiply a mistake
Bear in mind that a low multiple doesn't guarantee you a great stock. Some multiples are low for good reason -- value traps that can end up leading you to underperformance. Among the red flags to beware in companies with low multiples:

• Inconsistent earnings power
• Lots of debt
• Weak competitive positions

Low multiples are a generally a promising sign, but you should always follow up with your own due diligence.

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Longtime Fool contributor Selena Maranjian owns shares of Amgen. First Solar is a Motley Fool Rule Breakers recommendation. The Fool owns shares of Medtronic. Try our investing newsletters free for 30 days. The Motley Fool is Fools writing for Fools.