Refer to figures.
Aspect Ratio is the ratio of the blade’s average chord length to its span and may have a marked effect on lift production.

A high aspect ratio airfoil has a big span and a small chord, like a helicopter's rotor blade. High aspect ratio airfoils are inherently more efficient than low aspect ratio blades. They generate proportionally more lift at all angles of attack up to the critical, which occurs earlier. Thus, they tend to be aerodynamically more efficient.

• For simply-shaped airfoils, the Aspect Ratio is given by the formula: AR = Rotor Span / Mean Chord Line.
• For more complex airfoils, it is difficult to determine the mean chord line, thus it is given by the formula: AR = Rotor Span² / Rotor Planform Area.