Calculating the Surface Area : Volume Ratios

We now have all the information we need in order to calculate the surface area to volume ratios of an adult and of an infant.

This means that an adult has 0.26 cm² of surface area for each cm³ of volume whereas an infant has 1.32 cm² for each cm³ of volume. Since the body loses water through the skin, an infant's larger surface area to volume ratio means that they will dehydrate much quicker than an adult will.

Why is the Infant's Surface Area to Volume Ratio Higher than the Adult's?

As mentioned previously, we assumed that an infant was 1/5 of the size of an adult.

Since area is two dimensional, the area of an infant is (1/5)² of an adult's, which is 1/25.

Our calculations confirm this:
A_Adult / 25
= 17576 / 25
= 703.04
≈ A_Infant

Volume on the other hand is three dimensional, which means that the volume of an infant is (1/5)³ of an adult's, which is 1/125.

Our calculations also confirm this:
V_Adult / 125
= 66445 / 125
= 531.56
≈ V_Infant

Since the volume decreases more rapidly than the surface area, the surface area to volume ratio is higher for an infant than an adult.