But we'll just take it on faith right now that this is how we can figure out the volume of a cone. So given this, can we figure out an expression that relates volume to the height of the cone? Well, we could say that volume, and I'll do it in this blue color, the volume of water is what we really care about. The volume of water is going to be equal to 1 third times the area of the surface of the water, area of water surface times our height of the water, so times h. So how can we figure out the area of the water surface, preferably in terms of h? Well, we see right over here the diameter across the top of the cone is 4 centimeters, and the height of the whole cup is 4 centimeters. And so that ratio is going to be true at any depth of water. It's always going to have the same ratio between the diameter across the top and the height, because these are lines right over here.