Wing Loading, the ratio of airplane weight to wing area, generally in units of ounces per square foot for small planes, is a useful comparison for glide performance.   Usually lighter glides better.  However, this measure works best for the same class of plane where wing areas are similar.  Cube Loading is a measure which can be used over a broader range of aircraft size.  Weight scales as the cube of length.  Wing area multiplied by the square root of itself gives a number which scales as the cube of length. Thus, if we divide wing loading by the square root of wing area, we get a number with units of ounces per cubic foot, where both top and bottom scale as the cube of length, and this is called the Cube Loading.