Child Fever Calculator - Temperature Correction, Grading & Dosing

Two thresholds, three responses - rectal vs axillary and when to call the doctor

A thermometer reading means nothing without context. 37.8 C under the arm is a fever (corrected to 38.3 C rectal). 37.8 C rectally is not. And a 38.2 C in a 2-month-old demands an ER visit, while the same number in a 4-year-old usually just needs fluids and monitoring.

This calculator takes the raw thermometer reading, applies the correct site-specific adjustment, classifies the result against pediatric thresholds, and - if you enter the child's weight - provides approximate paracetamol and ibuprofen doses in milligrams and milliliters of standard syrup.

How to use this calculator - step by step

Select your child's age bracket - age determines the urgency of a fever. Infants under 3 months with any fever above 38.0 C need immediate medical attention.
Enter the thermometer reading - type the exact number shown on the display. Do not adjust it yourself.
Choose the measurement site - rectal, ear, forehead, underarm or oral. Each has a different correction factor.
Optionally enter the child's weight - this unlocks medication dosing (paracetamol 15 mg/kg, ibuprofen 10 mg/kg per dose).
Read the results - corrected temperature, fever classification, recommendation, and (if weight entered) dosing table.

Measurement site correction table

Every site except rectal underestimates core body temperature. The correction factors below convert any reading to its rectal equivalent.

Measurement site	Correction to rectal	Notes
Rectal	+0.0 C	Gold standard, most accurate
Ear (tympanic)	+0.2 C	Fast but earwax can distort
Oral	+0.3 C	Good for children 5+, wait 15 min after hot drinks
Forehead (infrared)	+0.4 C	Convenient but sensitive to room temperature and sweat
Underarm (axillary)	+0.5 C	Least accurate, requires 3-5 min hold, non-invasive

Fever classification in children (rectal equivalent)

Temperature (rectal)	Classification	Action
Below 36.0 C	Hypothermia	Warm the child, recheck
36.0-37.4 C	Normal	No intervention needed
37.5-37.9 C	Low-grade fever	Monitor, push fluids
38.0-38.9 C	Moderate fever	Medicate if child is uncomfortable
39.0-39.9 C	High fever	Antipyretic + doctor if not improving
40.0 C and above	Very high fever	Antipyretic + urgent medical attention

Real-world correction examples

Underarm reading: 37.2 C, child age 2 years
Corrected: 37.7 C (low-grade). No medication needed, just monitor and keep hydrated.

Forehead reading: 38.1 C, child age 8 months, weight 9 kg
Corrected: 38.5 C (moderate fever). Paracetamol dose: 135 mg (5.6 ml syrup). Ibuprofen: 90 mg (4.5 ml).

Ear reading: 39.3 C, child age 4 years, weight 16 kg
Corrected: 39.5 C (high fever). Paracetamol: 240 mg (10 ml). Ibuprofen: 160 mg (8 ml). Contact doctor if no improvement in 1 hour.

Rectal reading: 38.2 C, infant age 2 months
Corrected: 38.2 C (no correction needed). URGENT: Any fever in an infant under 3 months requires immediate medical evaluation.

Oral reading: 37.5 C, child age 10 years
Corrected: 37.8 C (low-grade). Borderline - recheck in 30-60 minutes. No medication unless the child feels unwell.

Frequently asked questions

What temperature is considered a fever in children?

38.0 C measured rectally is the standard threshold. For axillary (underarm) readings, 37.5 C indicates fever after adding the +0.5 C correction. For forehead: 37.6 C (+0.4 C correction). The important number is always the corrected rectal equivalent.

When should I give fever medication?

Not based on the number alone. Give medication when the child is uncomfortable, irritable, refusing fluids, or clearly in pain. A child at 38.5 C who is playing normally does not need medication. A child at 38.1 C who is lethargic and refusing drinks probably does. Treat the child, not the thermometer.

How much paracetamol per kilogram of body weight?

10-15 mg/kg per dose, every 4-6 hours, maximum 4 times per day. This calculator uses 15 mg/kg (upper single-dose limit). For a 12 kg child: 180 mg = approximately 7.5 ml of standard 120 mg/5 ml syrup. Maximum daily dose: 60 mg/kg.

From what age can children take ibuprofen?

From 6 months of age (and body weight above 7 kg). Dose: 5-10 mg/kg every 6-8 hours, max 3 times daily. This calculator uses 10 mg/kg. Do not give ibuprofen to children with chickenpox, dehydration, or known kidney issues. Avoid in infants under 6 months.

Is a high fever more dangerous than a moderate one?

Not necessarily. Fever height does not correlate with disease severity. A common cold can push temperature to 39.5 C, while a serious bacterial infection might only produce 38.3 C. What matters more: how the child looks and behaves (energy, hydration, responsiveness), not the exact number on the thermometer.

Can teething cause a fever?

Teething can raise temperature by 0.1-0.2 C, but it does not cause fever above 38.0 C. If a teething baby has a temperature of 38.5 C, look for another cause (infection, virus). The teething-fever myth persists because the teething window (6-24 months) overlaps with the age when children get their first round of common infections.

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