The ranges are due to the enormous stretchiness of the sheets. Hence, they will adjust to
the exact contours of your mattress and will accommodate your bed's size perfectly.
Exact Mattress Size Ranges for Queen, Queen XL Sheets are:
Width:   For Mattresses between 55" and 63" (inches) wide (140 to 160 centimeters)        
Length: For Mattresses between 78" and 87" (inches) long (200 to 220 centimeters)        
Depth:   For Mattresses between   6" and 18" (inches) deep (minimum and maximum
recommended mattress thickness) (15 to 45 centimeters)