Problem: Values between 0 and 4 returns Small. Values between 5 and 9 returns Medium. Values between 10 and 15 returns Large?

Solution:

Categorize numbers

Formula in cell B1:

=LOOKUP(A1,{0;5;10},{"SMALL";"MEDIUM";"LARGE"})

LOOKUP(lookup_value,array)
Looks up a value either from one-row or one-column range or from an array. Provided for backward compability.