Question

Why might you need measure a perimeter with a measuring tape instead of a ruler

Answer 1

Because a ruler is 4 times smaller minimum of mesuring tape

Answer 2

The perimeter may not be small enough to measure with just a ruler. For example, if a side of a rectangle was 30 inches, how would you use a 12 inch ruler to accurately measure that side? Also, if you were measuring a shape like a circle or oval, a tape measure is flexible.