Although many metrics are used to measure the value of a company, Cramer said special attention should be paid to its future prospects. After all, that's why investors are willing to pay more for growing companies with strong future prospects, even though they may seem more expensive than their slow-growing peers.

Take Pfizer and Celgene , for example. The former is currently selling for 8.6 times next year's earnings while Celgene sells for 14.5 times earnings. Pfizer may appear cheaper, but Cramer said it only has a lower multiple. While Pfizer yields 4 percent and has a big buyback, Cramer said it lacks growth and that means you can't justify paying up for this stock.