RE: Minimum sail size for Formula Exp 160
rgugli offers good advice, but what's missing is your skill level and experience. It's difficult to offer advice without this information.
I am a recreational sailor (23 years), but I have sailed and raced formula boards for 6 years. Sail size depends on board type, sailor weight, wind speed, water conditions, sailor experience, racing or recreational use & budget ($).
Provide some of the above information and we can offer better advice.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.