What is the formula for wing aspect ratio?

• A. Aspect ratio = wing span / average chord
• B. Aspect ratio = wing span / wing area
• C. Aspect ratio = wing area / span
• D. Aspect ratio = average chord / span

Answer: (A)

Aspect ratio is a measure of how slender a wing is, expressed as the wingspan relative to the average chord. The standard relationship is AR = b / c̄, where b is the wingspan and c̄ is the average chord. Since the wing area S ≈ b × c̄, this is also AR = b^2 / S. So the span divided by the average chord is the correct form.

Using span divided by wing area would mix a length with an area, yielding a quantity with units, not a dimensionless aspect ratio. Wing area divided by span gives a length, not AR. The ratio of average chord to span is the reciprocal of AR for common planforms, so it does not represent the aspect ratio itself.