Depends on size of the patio.
one yard of cement will make a 8 x 10 square foot slab at 4 inches thick, that's 80 sq. feet per yard of cement at 4 inches thick.
There is no easy answer to this question but the way to calculate the volume of gravel you need is to multiply the area of the driveway by the depth of the gravel your laying. You also need to make...
A good mix is four or five of sand to one of cement.
it depens how big the space is that u need to cover i would recomend 2 inches is enough