**5. Size selection**

Weight-based selection as per the manufacturer's guideline is done. If unsure, check the package cover for size information. More than one size should always be available, because the correct size cannot always be predicted. Weight-based selection has given way to sex-based selection, especially in adults. The consensus seems to be that the correct size would be a size 4 for most adult women and a size 5 for most adult men [51–57]. Whatever the initial size selected, if malposition or an inadequate seal is present, a larger size LMA should be considered. Alternative formulas based on weight have been proposed [58, 59]. For children, the width of the second to fourth fingers can be matched to the widest part of the mask [60]. If repeated attempts with one type of LMA are unsuccessful, changing to another type may help.
