1) Measure from the drain opening to the furthest wall, then round up to the nearest foot. Calculate the slope by multiplying the measurement by 1/4 inch. For instance, if the drain opening measures 2-foot 8-inches from the furthest wall, then the shower floor should slope 3/4 inch from that wall to the drain.Click to see full answer. Correspondingly, how do you find the slope in a shower? Step 1: Floor Tile Must Slope to the Drain In a stall shower, the plumbing code requires the floor be sloped one quarter (1/4) of an inch per foot in order to carry the water effectively to the drain. This slope, according to the TCNA Handbook is called “sloped fill” or commonly known as the pre-slope.Likewise, do you need a pre slope in a shower? No. I’ve installed a number of showers. There is no such thing as a ‘single step’ process. If you don’t have a pre-slope, or use something like Schluter’s drain pans (which is what I always use now), the water will pool and just sit there which will cause bacteria growth, possibly mold, etc. In this way, what should the slope of a shower floor be? Shower Floor Slope To efficiently drain, the recommended minimum slope for a shower floor is about 4 percent, or a 1/2 inch drop per every 12 inches from the shower walls to the drain. In traditional tile shower construction, this slope is established in the mortar pre-pan.What is a shower pre slope?The purpose of the slope in a shower pan is to encourage all water toward the drain. Under the tile and thin set is a sloped mortar base that creates the slope for you to lay your tile. Under that slope is the PVC liner which is on top of your preslope.