Subgrade strength, base thickness, concrete strength, slab thickness and safety factor all have effects that control the design of a floor. Often the designer must estimate or use suggested values. What if values are changed? Some changes have a drastic effect, while others have only a nominal effect. "What if" calculations can help refine designs. When subgrade modulus changes, slab thickness must increase or decrease. Adding a base course or increasing its thickness has only a slight effect on subgrade modulus. A small change in compressive strength has only a nominal effect on required slab thickness. Changing slab thickness has the most dramatic effect on the strength or load-carrying capacity of a floor. A change in the safety factor affects slab thickness and load-carrying capacity.