Enter the child’s weight and the adult dosage into the calculator to determine the child’s dosage. This calculator can also evaluate any of the variables given the others are known.

Clark’s Rule Formula

The following formula is used to calculate the dosage for children using Clark’s Rule.

Dc = (W * Da) / 150


  • Dc is the child’s dosage (mg) W is the child’s weight (lbs) Da is the adult dosage (mg)

To calculate the child’s dosage using Clark’s Rule, multiply the child’s weight by the adult dosage. Then, divide the result by 150. The result is the appropriate dosage for the child.

What is a Clark’s Rule?

Clark’s Rule is a medical formula used to calculate the dosage of medicine for children. It is based on the child’s weight in pounds. The rule states that the child’s dose is equal to the adult dose multiplied by the child’s weight in pounds, divided by 150 (the average adult weight). This rule is commonly used in pharmacology, however, it’s important to note that it’s not applicable for all medications and situations.

How to Calculate Clark’s Rule?

The following steps outline how to calculate the Clark’s Rule.

  1. First, determine the child’s weight (W) in pounds.
  2. Next, determine the adult dosage (Da) in milligrams.
  3. Next, use the formula Dc = (W * Da) / 150 to calculate the child’s dosage (Dc).
  4. Finally, calculate the Clark’s Rule.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Child’s weight (W) = 40 lbs

Adult dosage (Da) = 200 mg