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 in order 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

The nuances of the formula are explained in further detail here. 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 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 Amazon.com (Nasdaq: AMZN) and two 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

Amazon.com

(953.0%)

1110.3%

(145.8%)

(180.9%)

eBay (Nasdaq: EBAY)

15.9%

15.5%

12.3%

12.3%

Barnes & Noble (NYSE: BKS)

(1.0%*)

(0.9%)*

8.7%

10.2%

Overstock.com (Nasdaq: OSTK)

(17.4%)

(1.3%)

69.2%

(32.8%)

Source: Capital IQ, a division of Standard & Poor's. *Assumes 40% tax rate for comparison purposes.

Those negatives at Amazon look ominous, but they really aren't. They signify that Amazon had negative invested capital, not operating losses, which is a great position to be in. Negative invested capital means that Amazon effectively doesn't require capital to run its business. It's a similar situation at Overstock. The negative returns at Barnes & Noble, on the other hand, are due to operating losses, and the situation has clearly gotten worse over the last half-decade. eBay also turns in ROIC that tops our threshold for attractiveness and has even improved those numbers from five years ago.

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. If you'd like to add these companies to your Watchlist or set up a new Watchlist, just click here .

Jim Royal, Ph.D., does not own shares of any company mentioned. Amazon.com and eBay are Motley Fool Stock Advisor choices. 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.