parachute design

Hello, I already have diameter calculations for a small parachute: It is about 34 cm (13.38 inches). My only question is, how do you determine the number of gores a parachute must have? Is it more empirical?

I am developing parachutes to recover two mid-power rockets with predicted descent masses of about 140 grams (~5 oz) and 280 grams (~10 oz). On larger rockets I usually make toroidal chutes and use dual-deploy. On these rockets I am going to pop the main at apogee and use flat parachutes...

How to determine the no. of gores required for a parachute? Are there specific formula to determine this? Is it determined by obtaining the inflation shock value? I want to design an elliptical parachute with diameter=30''.. The material chosen is appox. 1.4 oz ripstop nylon NOTE: My question...