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 F5 Networks (Nasdaq: FFIV) 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.

F5 Networks has a P/E ratio of 34.3 and an EV/FCF ratio of 19.6 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 F5 Networks has a P/E ratio of 65.0 and a five-year EV/FCF ratio of 31.9.

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

F5 Networks 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

F5 Networks 34.3 19.6 65.0 31.9
Cisco Systems (Nasdaq: CSCO) 12.2 6.4 12.2 6.5
Citrix Systems (Nasdaq: CTXS) 40.5 21.8 61.5 32.5
Juniper Networks (NYSE: JNPR) 22.2 12.1 32.0 15.0

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

Numerically, we've seen how F5'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, F5's net income margin has ranged from 10.8% to 20.3%. In that same time frame, unlevered free cash flow margin has ranged from 24.7% to 33.9%.

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, F5 Networks 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, F5 Networks has put up past EPS growth rates of 28.7%. Meanwhile, Wall Street's analysts expect future growth rates of 24.8%.

Here's how F5 Networks compares with its peers for trailing five-year growth (because of losses, Juniper's trailing growth rate isn't meaningful):

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 F5 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 34.3 P/E ratio, and though its one-year EV/FCF ratio is a bit lower, its five-year price multiples are similarly high. For this premium price, we see strong margins and past growth with analyst expectations for more of it. If you find F5 Networks' numbers or story compelling, don't stop here. Continue your due-diligence process until you're confident one way or the other. As a start, add it to My Watchlist to find all of our Foolish analysis.

See the stocks that I've researched beyond the initial numbers and bought in my public real-money portfolio.

Anand Chokkavelu owns shares of Cisco. The Motley Fool owns shares of and has created a bull call spread position on Cisco Systems. Motley Fool newsletter services have recommended buying shares of Cisco Systems and shorting Juniper Networks. 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.