Scott Bryce has an excellent resource located at:
http://scottbryce.com/parachute/spherical_parachute.html
I routinely use the calculator to estimate the size of the parachute and then generate patterns and stich up my own. It has never let me down, except of course in the range that was intended!
Guessing your rocket will be around 8 pounds once the propellent has burned out. That would indicate an 86" diameter chute for 15 fps decent rate. It's worth mentioning that the parachutes that come with LOC kits are flat sheets and don't have nearly the drag that a properly stitched multigore spherical cute does. I size my chutes with a 6-12" spill hole (larger spill hole for a larger chute) using a 25% sphere. As for number of gores, I just play with it so it will mostly fit on a portrait sized 8.5 X 11" piece of paper. It will print out on multiple sheets, cut and tape together. I cut out a pattern on luan plywood which makes it very easy to cut the gores.
On the chutes I make, I use a quality serger with a 3 thread narrow seam stitch. It has worked very well for me. Either way, the calculator makes a great resource to size a parachute.
