Competency and proficiency in the calculation of drug doses are vital for the safety of neonates, infants and children. The margin for error is significant if a decimal point is misplaced and can have life-changing and life-threatening consequences for the child. Because the population that accesses children’s health care services includes both the premature neonate and the young adult, the range of doses prescribed is vast and varied. Drug calculations require basic numeracy skills.

Nearly all paediatric drug doses are calculated by weight, some by body surface area and some by age. When drugs are prescribed by weight, the weight will always be in kilograms (kg). You must ensure that the child has been prescribed the correct amount of drug for their weight. Some reference books will have a suitable range, minimum to maximum dose that may be safely prescribed. It is up to the prescriber to determine which dose they are prescribing and why.

• Local policy must be adhered to in relation to single or double checking.
  
• If there are two checkers, each should calculate the required drug amount independently.
  
• The ideal is that calculations are done in your head first, then answers may be checked with a calculator. Estimate, then guesstimate, then calculate.

There are two main formulas that are used. The first is the most commonly used: