It can be calculated by taking the square root of the wing span squared divided by the wing area. Higher aspect ratios mean longer wing spans. Longer wing spans displace more air in a given amount of forward motion. Sailplanes have aspect ratios of 16 to 20, Sport models are usually between 5 and 8, racing planes and scale jets can have aspect ratios as low as 1. A reminder as you approach high aspect ratios the average cord becomes small.
Small cords can run into structural problems and undesirable reynolds numbers .
Avoid tips with cords less than 5 inches. A tapered wing concentrates the strength of the wing near to the center. Tapered wings approximate elliptical wings and are thus slightly more efficient than are straight wings. A taper ratio of 0.4 most closely approximates the elliptical. Highly tapered wings can suffer undesirable reynolds numbers causing the tip of the wing to stall earlier than the root at low speeds.