An interesting headline caught my eye the other day: "Under Armour Larger Than S&P 500 component Ralph Lauren (NYSE:RL)." While this isn't a positive or negative headline on the surface, it did make me seriously consider the size of Under Armour (NYSE:UAA) at current levels and whether or not this is justified.

Although the Baltimore-based athletic apparel, footwear, and accessories maker is growing tremendously, the company's market capitalization gives it roughly the same size as fashion industry stalwarts Ralph Lauren and Coach (NYSE:TPR) and makes it almost twice as large as competitor lululemon athletica (NASDAQ:LULU).

The major aspect investors have to consider now is whether or not Under Armour deserves its current market capitalization. In order to determine this, it will help to compare the company to its competitors and its aforementioned peers of similar size.

Source: Company Facebook 

Sizing up the competition
The following table displays all four companies' current market caps as well as their fiscal 2013 revenue and their fiscal 2014 revenue estimates: 

CompanyMarket CapitalizationRevenue 2013Revenue 2014
Coach 13.35B 5.08B 4.89B
lululemon athetica 7.2B 1.37B 1.59B
Ralph Lauren 14.36B 6.94B 7.41B
Under Armour 12.03B 2.33B 2.88B

The data above highlights several important things. First is that, although the comparison is pretty close, Under Armour is not larger than Coach or Ralph Lauren at the current time. However, the market capitalizations of all three companies are close enough to warrant further comparison.

Under Armour is only projected to generate revenue of $2.88 billion in 2014, which is roughly half of the revenue generated by Coach and about one-third of the revenue generated by Ralph Lauren in fiscal 2014. However, Under Armour has the fastest projected sales growth of 23.7% for 2014, which compares very favorably to the 6.8% projection for Ralph Lauren. Coach is not even expected to grow its sales at all in 2014; in fact, the company is projected to experience a revenue decline of 3.7% for the year.

Additionally, Under Armour is not quite double the size of lululemon athletica. However, once again the comparison is interesting. Lululemon is expected to show 15.9% sales growth in fiscal 2014, which is impressive, although it's not close to Under Armour's 23.7% rate.

The data above tells us that the businesses of Coach and Ralph Lauren are more mature than those of Under Armour and lululemon. As a result, Ralph Lauren and Coach are able to generate much more sales but they are not growing as fast as these peers, or in Coach's case, not growing at all.

Lululemon is the more interesting company here because it is still relatively small and it has been growing quite well. The company's forward P/E of 22.53 is also much less extreme than Under Armour's 48.98. Investors seeking value alongside growth might do well to consider lululemon at current levels.

Bottom line
What this means for investors is that size, as judged by market capitalization, is relatively meaningless. This metric, by itself, should therefore not be used to make investment decisions.

Although it is roughly the same size as Ralph Lauren and Coach, Under Armour is growing significantly faster. It therefore remains the only large-cap company out of the bunch that serious growth investors should consider. Lululemon also appears to be worth considering as a relatively cheap mid-cap growth stock.

With an exciting business mix and vast international potential, Under Armour remains my largest equity position as well as my top growth pick for the next decade.