We'd all like to invest like the legendary Warren Buffett, turning thousands into millions or more. Buffett analyzes companies by calculating return on invested capital (ROIC) to help determine whether a company has an economic moat -- the ability to earn returns on its money above 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, it divides a company's operating profit by how much investment it took to get that profit. The formula is:

ROIC = Net operating profit after taxes / Invested capital

(You can read more about the nuances of the formula.)

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 it provides you with an apples-to-apples way to evaluate businesses, even across industries. The higher the ROIC, the more efficient 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 is between 8% and 12%. Ideally, we want to see ROIC above 12%, at a minimum, and a history of increasing returns, or at least steady returns, which indicate some durability to the company's economic moat.

Let's take a look at ResMed (NYSE: RMD) and three of its industry peers, to see how efficiently they use cash. Here are the ROIC figures for each company over a few periods.

Company

TTM

1 Year Ago

3 Years Ago

5 Years Ago

ResMed 18% 17.8% 12.6% 13.7%
Accuray (Nasdaq: ARAY) (9.9%)* 0.2%* 2% (27%)
CONMED (Nasdaq: CNMD) 5% 4.6% 6.5% 4.5%
Varian Medical Systems (NYSE: VAR) 41.7% 40% 36.1% 46.4%

Source: S&P Capital IQ.
*Because Accuray did not report an effective tax rate, we used its 33% rate from five years ago.

ResMed's returns on invested capital have gradually increased over the past three years and are more than 4 percentage points above what they were five years ago. Two of the other companies have also shown improvement in their returns from five years ago, while Varian's ROIC has declined by almost 5 percentage points. However, its ROIC is much higher than the other listed companies, suggesting that it has a fairly strong competitive position.

Businesses with consistently high ROIC show that they're efficiently using capital. They also have the ability to treat shareholders well, because they can then use their extra cash to pay out dividends to us, buy back shares, or further invest in their franchise. And healthy and growing dividends are something that Warren Buffett has long loved.

So for more successful investments, dig a little deeper than the earnings headlines to find the company's ROIC. Add these companies to your Watchlist:

Jim Royal, Ph.D., owns no shares of any company mentioned here. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.