Here at Zacks, our focus is on the proven Zacks Rank system, which emphasizes earnings estimates and estimate revisions to find great stocks. Nevertheless, we are always paying attention to the latest value, growth, and momentum trends to underscore strong picks.Considering these trends, value investing is clearly one of the most preferred ways to find strong stocks in any type of market. Value investors rely on traditional forms of analysis on key valuation metrics to find stocks that they believe are undervalued, leaving room for profits.Luckily, Zacks has developed its own Style Scores system in an effort to find stocks with specific traits. Value investors will be interested in the system's "Value" category. Stocks with both "A" grades in the Value category and high Zacks Ranks are among the strongest value stocks on the market right now.One company value investors might notice is Graphic Packaging Holding Company (GPK). GPK is currently sporting a Zacks Rank of #2 (Buy), as well as a Value grade of A. The stock holds a P/E ratio of 9.09, while its industry has an average P/E of 12.75. Over the past year, GPK's Forward P/E has been as high as 17.63 and as low as 8.29, with a median of 9.70.Investors should also recognize that GPK has a P/B ratio of 3.57. Investors use the P/B ratio to look at a stock's market value versus its book value, which is defined as total assets minus total liabilities. This company's current P/B looks solid when compared to its industry's average P/B of 9.08. Within the past 52 weeks, GPK's P/B has been as high as 3.85 and as low as 2.95, with a median of 3.31.Value investors also use the P/S ratio. The P/S ratio is is calculated as price divided by sales. Some people prefer this metric because sales are harder to manipulate on an income statement. This means it could be a truer performance indicator. GPK has a P/S ratio of 0.78. This compares to its industry's average P/S of 0.85.Finally, investors will want to recognize that GPK has a P/CF ratio of 7.32. This metric takes into account a company's operating cash flow and can be used to find stocks that are undervalued based on their solid cash outlook. This company's current P/CF looks solid when compared to its industry's average P/CF of 23.89. Over the past year, GPK's P/CF has been as high as 9.12 and as low as 6.35, with a median of 8.33.These figures are just a handful of the metrics value investors tend to look at, but they help show that Graphic Packaging Holding Company is likely being undervalued right now. Considering this, as well as the strength of its earnings outlook, GPK feels like a great value stock at the moment. Zacks Names "Single Best Pick to Double" From thousands of stocks, 5 Zacks experts each have chosen their favorite to skyrocket +100% or more in months to come. From those 5, Director of Research Sheraz Mian hand-picks one to have the most explosive upside of all. It’s a little-known chemical company that’s up 65% over last year, yet still dirt cheap. With unrelenting demand, soaring 2022 earnings estimates, and $1.5 billion for repurchasing shares, retail investors could jump in at any time. This company could rival or surpass other recent Zacks’ Stocks Set to Double like Boston Beer Company which shot up +143.0% in little more than 9 months and NVIDIA which boomed +175.9% in one year.Free: See Our Top Stock and 4 Runners Up >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Graphic Packaging Holding Company (GPK): Free Stock Analysis ReportTo read this article on Zacks.com click here.Zacks Investment Research