Check the label on your bottle to confirm concentration.
Low (5 mg/kg) – Temperature < 102.5°F
High (10 mg/kg) – Temperature > 102.5°F
Standard pediatric range is 5-10 mg per kg of body weight.
Recommended Single Dose
—
— mg active ingredient
Frequency
Every 6-8 Hours
Max Daily Dose (24h)
— mg
Max Daily Volume/Count
—
⚠️ Medical Disclaimer: This tool is for educational purposes only. Always consult a pediatrician before administering medication. Do not exceed 4 doses in 24 hours.
Figure 1: Comparison of Low vs. High Dosage for Input Weight
Dosage Reference Table (Based on Selected Product)
Weight
Low Dose (5mg/kg)
High Dose (10mg/kg)
Max Daily (40mg/kg)
What is Motrin Calculation by Weight?
Motrin calculation by weight is the clinical standard for determining the safe and effective dosage of ibuprofen for children. Unlike adult medications which often have fixed dosages, pediatric medicine relies heavily on the child's body mass to ensure safety. Giving a dose based solely on age can be dangerous because children of the same age can vary significantly in weight.
This calculation ensures that the child receives enough medication to be effective against pain or fever (therapeutic level) without reaching toxic levels. Ibuprofen (the active ingredient in Motrin and Advil) has a narrow therapeutic index in children, meaning accuracy is critical.
Note: Pediatricians almost universally recommend dosing by weight rather than age. If you do not know your child's current weight, weigh them before administering medication.
Motrin Calculation by Weight Formula
The mathematical foundation for pediatric ibuprofen dosage is straightforward but requires careful attention to units. The standard safe dosage range is 5 mg to 10 mg of ibuprofen per kilogram of body weight.
The Core Formula
To find the total milligrams (mg) needed:
Total Dose (mg) = Weight (kg) × Target Dosage (mg/kg)
To convert that into milliliters (mL) of liquid medicine:
Volume (mL) = Total Dose (mg) ÷ Concentration (mg/mL)
Variables Explained
Variable
Meaning
Unit
Typical Range
Weight
Child's body mass
kg (or lbs / 2.2)
5kg – 50kg+
Target Dosage
Strength of dose
mg/kg
5 mg/kg (Low) – 10 mg/kg (High)
Concentration
Medicine strength
mg/mL
20mg/mL or 40mg/mL
Practical Examples of Motrin Calculation by Weight
Example 1: A Toddler with High Fever
Scenario: A 2-year-old child weighs 28 lbs and has a high fever (over 102.5°F). You have Children's Suspension (100mg/5mL).
Convert Weight: 28 lbs ÷ 2.205 = 12.7 kg.
Determine Target Dose: High fever requires 10 mg/kg.
Calculate Total Mg: 12.7 kg × 10 mg/kg = 127 mg.
Calculate Volume: The concentration is 100mg per 5mL (which is 20mg/mL). 127 mg ÷ 20 mg/mL = 6.35 mL.
Result: You would administer approximately 6.3 mL or 6.4 mL.
Example 2: An Older Child with Mild Pain
Scenario: An 8-year-old weighs 60 lbs and has mild muscle soreness. You have Chewable Tablets (50mg each).
Convert Weight: 60 lbs ÷ 2.205 = 27.2 kg.
Determine Target Dose: Mild pain usually requires 5 mg/kg.
Result: Since you cannot easily split tablets into 0.72, you would likely round down to 2.5 tablets (125mg) or consult a doctor for rounding guidance.
How to Use This Motrin Calculation by Weight Calculator
Follow these steps to ensure an accurate result:
Enter Weight: Input the child's current weight. Use the toggle to switch between pounds (lbs) and kilograms (kg).
Select Product: Look at your medicine bottle. Is it "Infant Drops" or "Children's Suspension"? Select the exact match.
Select Dosage Strength: Choose 5 mg/kg for mild pain/fever or 10 mg/kg for high fever.
Read Results: The calculator displays the exact volume (mL) or tablet count, along with the total milligrams.
Check Max Daily: Ensure the total amount given in 24 hours does not exceed the "Max Daily Dose" displayed.
Key Factors That Affect Motrin Calculation by Weight
Several variables influence the final motrin calculation by weight and the safety of the dosage:
Hydration Status: Ibuprofen is processed by the kidneys. Dehydrated children (common with fever) are at higher risk of kidney stress. Ensure the child is drinking fluids.
Age vs. Weight: While weight is the primary factor, ibuprofen is generally not recommended for infants under 6 months unless directed by a doctor.
Concentration Confusion: Different countries and brands have different concentrations. In the US, infant drops used to be more concentrated than children's liquid, but this has largely been standardized to 100mg/5mL to prevent errors. Always check the label.
Frequency: Ibuprofen lasts longer than acetaminophen (Tylenol). It should be given every 6 to 8 hours, not every 4 hours.
Underlying Conditions: Children with kidney disease, asthma, or stomach ulcers may need adjusted dosages or should avoid ibuprofen entirely.
Combination Medicines: Many cold and cough syrups contain ibuprofen. Calculating a separate dose while using these products can lead to accidental overdose.
Frequently Asked Questions (FAQ)
Can I round up the result from the motrin calculation by weight?
It is generally safer to round down for mild symptoms. For high fever, pediatricians may allow rounding to the nearest measurable increment, but never exceed the maximum daily limit of 40mg/kg.
What is the maximum daily dose of Motrin for a child?
The maximum daily dose is typically 40 mg per kg of body weight per day, or 4 doses in a 24-hour period, whichever is lower.
Can I alternate Motrin and Tylenol?
Yes, many pediatricians allow alternating acetaminophen and ibuprofen every 3-4 hours for stubborn fevers, but this increases the risk of dosing errors. Keep a written log of times and dosages.
Is the motrin calculation by weight different for adults?
Yes. Adults usually take fixed doses (200mg to 800mg) because their metabolism and liver/kidney function are mature. Pediatric dosing is strictly weight-based.
What if my child vomits after the dose?
If the child vomits within 15 minutes, you may usually redose. If it has been longer than 15-20 minutes, do not redose, as some medication may have been absorbed.
Why is the infant drop concentration important?
Historically, infant drops were more concentrated (50mg/1.25mL) than children's liquid (100mg/5mL). Using the wrong calculation could lead to a massive overdose. Always verify the concentration on the bottle.
Does this calculator work for Advil?
Yes. Motrin and Advil both use the active ingredient ibuprofen. As long as you match the concentration on the bottle, the calculation is the same.
Is 10mg/kg safe for all children?
10mg/kg is the upper limit for a single dose, usually reserved for high fevers (>102.5°F). For mild pain, 5mg/kg is often sufficient and places less stress on the kidneys.