We'd all like to invest as successfully as the legendary Warren Buffett. He calculates return on invested capital to help determine whether a company has an economic moat -- the ability to earn returns on its money beyond that money's cost.

ROIC is perhaps the most important metric in value investing. By determining a company's ROIC, you can see how well it's using the cash you entrust to it, and whether it's actually creating value for you. Simply put, ROIC divides a company's operating profit by the amount of investment it took to get that profit:

ROIC = Net operating profit after taxes / Invested capital

This one-size-fits-all calculation cuts out many of the legal accounting tricks (such as excessive debt) that managers use to boost earnings numbers, and provides you with an apples-to-apples way to evaluate businesses, even across industries. The higher the ROIC, the more efficiently the company uses capital.

Ultimately, we're looking for companies that can invest their money at rates that are higher than the cost of capital, which for most businesses lands between 8% and 12%. Ideally, we want to see ROIC greater than 12%, at minimum. We're also seeking a history of increasing returns, or at least steady returns, which indicate that the company's moat can withstand competitors' assaults.

Let's look at Rio Tinto (NYSE: RIO) and two of its industry peers to see how efficiently they use capital. Here are the ROIC figures for each company over several time periods:

Company

TTM

1 Year Ago

3 Years Ago

5 Years Ago

Rio Tinto 15.7%

12.5%

21.0%

14.2%

BHP Billiton (Nasdaq: BHP) 26.3%

14.0%

27.7%

17.0%

Vale (NYSE: VALE) 18.8%

6.3%

19.2%

28.9%

Source: Capital IQ, a division of Standard & Poor's. *Uses the TTM effective tax rate of 38%.       

All of these companies surpass our 12% threshold for returns on invested capital, but Vale has shown a substantial decline in its ROIC from five years ago. Rio Tinto has shown slight increases in its ROIC from five years ago, but BHP Billiton's ROIC has increased substantially in the same amount of time.

Businesses with consistently high ROIC are efficiently using capital. They can use their extra returns to buy back shares, further invest in their future success, or pay dividends to shareholders. (Warren Buffett especially likes that last part.)

To unearth more successful investments, dig a little deeper than the earnings headlines, and check up on your companies' ROIC.

Jim Royal, Ph.D., does not own shares in any company mentioned here. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.