Body Surface Area (BSA)


Infants and children are small size bodies and their body function cannot tolerate adult medications which is why amount of drug is reduced compare to adult doses. Infants body systems are not fully developed and they lack the enzymes necessary to metabolize drugs. A child's volume of total body water will not distribute medications at a adult dose so this leads to reduce dose. Infants and children can receive medications at any route. Using the BSA calculation can determine correct dosages for children and infants. Body surface area (BSA) is a measurement of the surface of the body using height and weight.


There are a few formulas to calculate BSA but there is one formula recommended to use it's called

"The Mostellar Formula"

                     OR                    BSA () =   *wt(Lbs), ht(in)


1. A child weighs 27 pounds (Lbs) and is 30 inches (in) tall. What is the BSA of the child?

 > In your calculator input the following information given in the question according to formula.

27 Lbs X 30 inches / 3131 = 0.258....

*Next you have to square meter to get your BSA for your final answer

(Hit the button, then hit the  button after you do that input 0.258, click enter = 0.51

2. 60 cm, 25kg. What is the BSA?

60 cm X 25 kg / 3600 = 0.416...

Hit   and   then input 0.416 = 0.64  



                   Now I will easily show you how to use a namogram BSA chart, it may take some practice!




                                                                    The purpose of a namogram is to measure the total surface area in square meters (m²).

Example 1. A child weighs 55 lbs and is 85 cm tall. Determine this child's BSA using the namogram.

> First find and mark the child's height in the first column (height cm/in).

> Second find and mark the child's weight in the fourth/last column (weight lb/kg).


                           Then use a ruler to align the marks, then look on the BSA column to read the BSA mark for your final answer.


 Final answer for BSA is 0.82

  Sometimes a question may ask to determine BSA if a child is of normal height and weight which is 32lbs in this case. All you have to do is look for 32lbs in the second column of the namogram (For Children of Normal Height for Weight) and the answer is align across from it.

Answer: 0.62

   Child is 30 in, weighs 27 lbs. Use namogram to determine BSA.

( **You can print the namogram chart to practice, use a pencil so you can easily erase your mistakes)

Answer: 0.54



     Here is a formula used when calculating BSA with an adult dose

                                                                              BSA of patient in      X adult dose = desired dose

A child weighs 55 lbs and is 85 cm tall. The physician orders amoxicillin to BSA for the child. Previously you determined that the BSA for this child on the namogram is 0.82
m². The adult dose is 500 mg. What is the dose for the child?

    X 500 mg = 241 mg