How much should a 40 year old man weight standing 6 ft tall?

About 140-180 lbs: I can't stress enough that overall healthy habits (not smoking, physical inactivity, heart disease, etc.) are often shown to be more important than absolute weight; however, to answer your question, the "normal" range for a 6' tall male is about 140-180 pounds. "overweight" is considered 185-215 pounds. "obese" is considered greater than 220 pounds. Hope that helps!