There is some ambiguity about the meaning of "seat width". It can be taken as the width enclosed by the armrests on each side, i.e., the width available to sit in, or as the distance from the midpoint of one armrest to the midpoint of the next, a larger figure by the width of an armrest, and the width available for the shoulders (it is also one-third of the width of a block of three identical seats). It is thought that most airlines use the first of these figures.[15] In Economy class this width was typically 43 to 46 centimeters (17 to 18 in) in 2003.[16]