Land's End has typical measurements for a woman's size 18. The bust is 43 inches, the waist is 36 1/2 to 37 1/2 inches and the hips are 46 inches. A size 18 is typically considered an extra-large.
Arm length varies for size 18 garments depending upon the fit. For petite styles, the length is 31 1/8 inches. Tall tops have sleeves that run 33 3/8 inches. Regular fit sleeves are 32 3/8 inches long. According to Discovery, size measurements often vary among manufacturers and are constantly changing. To attract customers, manufacturers lower sizes. For instance, in 1997, a size 8 was the same as a size 10 was a decade before.