This web page will produce patterns for hemisphere parachutes for model rockets. Instructions for constructing the parachutes can be found in the May/June 2000 newsletter of the Northern Illinois Rocketry Association.
The article describes the construction of 12 inch diameter parachute with 8 gores and a 2 inch diameter spill hole. This web page will produce patterns for other sizes of parachutes.
As you are considering the size of your parachute, keep in mind that a spherical parachute has twice the drag coefficient of a comparable sized parasheet style parachute that comes with most model rocket kits.
Parachute shroud lines should be 1 1/2 times the diameter of the parachute.
Patterns include a 1/4 inch seam allowance.
Please check your print settings before printing the pattern. Acrobat Reader will resize an oversized pattern to fit the page by default. If your pattern is larger than your page, you may have to select a larger paper size, and/or create your parachute with more gores.