If you will go to some of the rocketry forums such as www.rocketryforum.com or go to some of the chute manufacturers websites such as top flite or fruity chutes, ( and there are links on this website that can take you there) a number of these makers will have the information you are seeking. There are several experts in the club that might chime in also. I have learned also, that there is not one set rule. Decent rate of your rocket is not only controlled by the weight of the rocket, but what is the altitude of the ground base you are launching from. If I am launching at sea level I can use a smaller chute than what I am using at our launch sites, and if I am going to launch at Hartsel, which is 3000 feet higher than us here in Northern Colorado, I need an even bigger chute. Also the design of the chute is important for decent rate. If I use a toroidal chute, it will come down slower than if I use an "X" chute or a parabolic chute. And there are lots of chute designs, square, round, hemispherical, toroidal, X, flat sheet, etc. I thought it was a simple answer until I started asking questions and doing computer research on the topic. I am attempting to make my own soon, and have a mentor on this also.

Can't add anything to what Bear says and I'm certainly no expert, but have an example of how 'not simple' it can get. I built a little Estes kit with 'enhancements' - shock cord upgrade, reinforced payload bay, etc. Without much thought I replced the 8" plastic with a 10" nylon - extra weght and all. My E9 flight went 1400' high and 4800' downwind in nearly calm conditions. Descent took 6 minutes. Lucky I found it. Cut a 2" spill hole in the parachute and now it works fine - but for me, it's still more art than science.