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 Single, Twin, Single XL, Twin XL Sheets are:
Width:   For Mattresses between 35" and 40" (inches) wide (90 to 100 centimeters)        
Length: For Mattresses between 75" and 87" (inches) long (190 to 220 centimeters)        
Depth:   For Mattresses between   4" and 16" (inches) deep (minimum and maximum
recommended mattress thickness) (10 to 40 centimeters)
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