Numbers can lie -- yet they're the best first step in determining whether a stock is a buy. In this series, we use some carefully chosen metrics to size up a stock's true value based on the following clues:

• The current price multiples.
• The consistency of past earnings and cash flow.
• The amount of growth we can expect.

Let's see what those numbers can tell us about how expensive or cheap Costco Wholesale (Nasdaq: COST) might be.

The current price multiples
First, we'll look at most investors' favorite metric: the price-to-earnings ratio. It divides the company's share price by its earnings per share (EPS). The lower the P/E, the better.

Then we'll take things up a notch with a more advanced metric: enterprise value to unlevered free cash flow. This tool divides the company's enterprise value (basically, its market cap plus its debt, minus its cash) by its unlevered free cash flow (its free cash flow, adding back the interest payments on its debt). As with the P/E, the lower this number is, the better.

Analysts argue about which is more important -- earnings or cash flow. Who cares? A good buy ideally has low multiples on both.

Costco has a P/E ratio of 24.3 and an EV/FCF ratio of 17.0 over the trailing 12 months. If we stretch and compare current valuations with the five-year averages for earnings and free cash flow, we see that Costco has a P/E ratio of 27.5 and a five-year EV/FCF ratio of 28.5.

A one-year ratio of less than 10 for both metrics is ideal. For a five-year metric, less than 20 is ideal.

Costco is 0-for-4 on hitting the ideal targets, but let's see how it stacks up against some of its competitors and industry mates.

Company

1-Year P/E

1-Year EV/FCF

5-Year P/E

5-Year EV/FCF

Costco 24.3 17.0 27.5 28.5
Wal-Mart (NYSE: WMT) 13.2 16.7 15.1 24.6
Target (NYSE: TGT) 13.7 12.6 14.6 24.2
Amazon.com (Nasdaq: AMZN) 74.1 30.4 126.8 44.6

Source: Capital IQ, a division of Standard & Poor's; NM = not meaningful.

Numerically, we've seen how Costco's valuation rates on both an absolute and relative basis. Next, let's examine …

The consistency of past earnings and cash flow
An ideal company will be consistently strong in its earnings and cash-flow generation.

In the past five years, Costco's net income margin has ranged from 1.5% to 1.8%. In that same time frame, unlevered free cash flow margin has ranged from 0.6% to 2.4%.

How do those figures compare with those of the company's peers? See for yourself:

Source: Capital IQ, a division of Standard & Poor's; margin ranges are combined.

In addition, over the past five years, Costco has tallied up five years of positive earnings and five years of positive free cash flow.

Next, let's figure out …

How much growth we can expect
Analysts tend to comically overstate their five-year growth estimates. If you accept them at face value, you will overpay for stocks. But even though you should definitely take the analysts' prognostications with a grain of salt, they can still provide a useful starting point when compared with similar numbers from a company's closest rivals.

Let's start by seeing what this company's done over the past five years. In that time period, Costco has put up past EPS growth rates of 6.4%. Meanwhile, Wall Street's analysts expect future growth rates of 13.4%.

Here's how Costco compares with its peers for trailing five-year growth:

Source: Capital IQ, a division of Standard & Poor's; EPS growth shown.

And here's how it measures up with regard to the growth analysts expect over the next five years:

Source: Capital IQ, a division of Standard & Poor's; estimates for EPS growth.

The bottom line
The pile of numbers we've plowed through has shown us the price multiples that shares of Costco are trading at, the volatility of its operational performance, and what kind of growth profile it has -- both on an absolute and a relative basis.

The more consistent a company's performance has been and the more growth we can expect, the more we should be willing to pay. We've gone well beyond looking at a 24.3 P/E ratio, and we see some solid numbers for Costco and each of its competitors. Costco is selling for a premium over Wal-Mart and Target for similar growth, whereas Amazon is more pricey still, because of its rapid growth trajectory. All have shown consistent profitability. If you find Costco's numbers or story compelling (or those of any of the others), don't stop here. Continue your due-diligence process until you're confident that the initial numbers aren't lying to you.

Interested in reading more about any of these stocks? Add them to My Watchlist to find all of our Foolish analysis. And for more stock ideas, check out this recent article: "The Only Stocks You'll Need to Retire."

Anand Chokkavelu doesn't own shares in any company mentioned. Costco and Wal-Mart are Motley Fool Inside Value picks. Amazon.com and Costco are Motley Fool Stock Advisor recommendations. Wal-Mart is a Motley Fool Global Gains choice. The Fool owns shares of Costco and Wal-Mart. 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.