Most of the people in construction are well aware that a 2x6 is much stronger than a 2x4. But how much stronger? The answer is simple. The bending strength of a beam increases with the square of the depth. Comparing the 2x4 and the 2x6: 4 squared is 16, 6 squared is 36, so the bending strength of the 2x6 is 36/16 times that of the 2x4. The ratio is 2.25, which means the 2x6 has 225 percent of the strength of a 2x4. How this all applies to concrete is a rather simple: strength of a concrete slab on grade increases much faster than cost, when increases are made in slab thickness. The final conclusion of the article is: for every dollar that is spent to produce a thicker floor you get more than twice as much value in actual load carrying capacity.