When it looks bowly waist to chest and nobody is out, it's probably 6-8 ft and heaving thus nobody is out. After 20 years of surfing this is a rule I forget time and time again. Needless to say my 5'5 twin fin was not the right call and I got my ass handed to me on almost every wave. One beating was so bad it pulled my wetsuit sideways, like a 90 degree turn, uncomfortable and had I not been alone, mildly embarrassing.