Looks like 1/8 to 1/4 inch per foot
From Askthebuilder.com:
Quote:
A typical ceramic tile shower has a cement mortar base that is just beneath the tile. The thickness of this mortar system can be as little as 1 to 1.5 inches. If you have ever used one of these showers, you know the slope does not have to be significant for water to find its way to the drain. The shower area floor simply needs to slope 1/8 inch per foot to achieve excellent drainage.
and from the tiledoctor.com:
Quote:
The other critical element is that the floor below the membrane must be sloped 1/4" to the foot toward the drain.