Weight-based medication
mg/kg → mL
Use a verified mg/kg order, documented weight and liquid concentration to calculate the volume per dose.
Calculate mg/kg dosePaediatric calculations
Paediatric medication & fluid calculations
Start with the documented weight and the exact order or fluid question in front of you. Calculate the arithmetic, understand the pathway, then practise the same skills step by step.
Documented weight first
Units stay visible
Formula ≠ prescription
5 calculators4 guides2 Learn pathways
Two core paediatric pathways
Medication dose
Weightkg
×Dose ratemg/kg
→Dosemg
Dose (mg) ÷ concentration (mg/mL) → volume to give (mL)
Maintenance-fluid estimate
Weightkg
→4-2-1mL/hr
100-50-20mL/day
These are arithmetic estimates of standard full maintenance, not a choice of fluid or an individual prescribing plan.
Before using a paediatric result
Confirm the current documented weight, order wording, dose frequency, medicine concentration, maximum-dose limits and local paediatric guidance. A correct calculation does not validate the prescription or determine the clinical plan.
Calculate now
What are you trying to work out?
Start with the exact order, fluid question or protocol requirement. The first two cards cover the most specifically paediatric workflows.
Maintenance fluids
4-2-1 & 100-50-20
Calculate common hourly and daily full-maintenance estimates from the patient's documented weight.
Calculate maintenance fluidsDose already in mg
mg → mL
Convert an already-prescribed milligram dose into a measurable liquid volume from the verified medicine strength.
Calculate mLProtocol uses body surface area
BSA (m²)
Calculate body surface area when the medication or protocol explicitly requires a named BSA equation.
Calculate BSASolid oral dose
Tablet dosing
Convert a verified prescribed dose into tablets when the specific medicine and formulation are suitable for tablet dosing.
Calculate tabletsUnderstand
Understand the calculation before applying it
The Guides explain why the arithmetic works, where the boundaries sit and which common mistake changes the answer.
Paediatric medication maths
Weight-Based Medication Dosing
Follow mg/kg wording from patient weight to the prescribed amount and final liquid volume.
Read GuideFluid calculations
Paediatric Maintenance Fluids Explained
Understand the 4-2-1 hourly and 100-50-20 daily rules, where they come from and how they differ.
Read GuideProtocol-based dosing
BSA Medication Dosing (mg/m²)
Keep the patient's BSA in m² separate from the medication order written in mg/m².
Read GuideDose safety
Safe Dose Ranges & Maximum Doses
Learn how supplied safe ranges and maximum-dose limits fit around the arithmetic rather than replacing the order check.
Read GuideLearn
Learn the paediatric pathways
0102
Open Paediatric Calculations topic Paediatric Dose Calculation Pathway
Work through weight, mg/kg wording, supplied dose-range checks and the final dose-to-volume step in one visible chain.
Open lessonPaediatric Maintenance Fluids
Learn the common 4-2-1 hourly and 100-50-20 daily full-maintenance arithmetic without confusing the estimate with a clinical prescription.
Open lessonPractice
Practise until the sequence is automatic
Each quiz opens the full Foundations → Beginner → Intermediate → Advanced pathway.
Common paediatric calculation mistakes
The arithmetic can be right while the setup is wrong
Wrong or outdated weight
Use the current documented weight required by the medication order or protocol. Do not substitute an estimated or remembered weight.
Per dose vs per day
Keep mg/kg/dose and mg/kg/day visibly separate. Daily orders may need a separate divided-dose step before converting to mL.
Missing maximum-dose check
A mathematically correct weight-based result can still exceed a supplied maximum dose. Check the medication reference and prescription.
Maintenance estimate treated as a prescription
4-2-1 and 100-50-20 calculate standard full-maintenance estimates only. They do not choose the fluid, tonicity, deficit replacement or final clinical plan.
BSA used automatically
Use BSA only when the medication, protocol or clinical reference explicitly requires a BSA-based method.