How to Use a Thermometer: A Step-by-Step Guide

Getting an accurate temperature reading is one of the most important skills for parents. Here’s everything you need to know about taking your child’s temperature safely and correctly.

Which Thermometer Should I Use?

Digital Thermometers (Best Choice)

Pros: Fast, accurate, affordable, easy to read
Cons: None—this is what pediatricians recommend
Cost: $5-15
Where to buy: Any pharmacy or grocery store

Temporal Artery (Forehead) Thermometers

Pros: Very fast, non-invasive, great for squirmy kids
Cons: Can be less accurate if not used correctly; expensive
Cost: $30-50
Best for: Toddlers and older children

Ear (Tympanic) Thermometers

Pros: Fast and fairly accurate
Cons: Ear wax can affect accuracy; doesn’t work well in babies under 6 months
Cost: $20-40
Best for: Children over 6 months

❌ Not Recommended:

Pacifier thermometers – Inaccurate
Forehead strips – Unreliable
Glass mercury thermometers – Dangerous if broken (if you have one, dispose of it safely)

Which Method Should I Use?

The best method depends on your child’s age:

Age	Best Method	Why
Birth to 3 months	Rectal	Most accurate for infants
3 months to 4 years	Rectal (most accurate) or forehead (easier)	Rectal is gold standard, but forehead works if done correctly
4 years and up	Oral or forehead	Kids can hold thermometer under tongue
Any age (quick check)	Underarm	Least accurate but good for screening

How to Take a Temperature: Step-by-Step

🔴 RECTAL (Most Accurate for Babies)

What you need:

Digital thermometer (label it “rectal only”)
Petroleum jelly (like Vaseline)
Diaper or towel

Steps:

Clean the thermometer with rubbing alcohol or soap and water
Apply a small amount of petroleum jelly to the tip
Position your baby:
- Lay baby on back with legs bent toward chest, OR
- Lay baby tummy-down across your lap
Insert gently: Insert the thermometer tip about ½ to 1 inch into the rectum (stop if you feel resistance)
Hold in place: Keep the thermometer and your baby still for about 1 minute or until it beeps
Read and record the temperature
Clean thoroughly with soap and water or alcohol

Tips:

Never force it—if there’s resistance, stop
Distract baby with a toy or song
It’s okay if baby cries—it’s uncomfortable but not painful
Mark this thermometer “rectal” so you never use it orally

Fever = ≥100.4°F (38°C) rectal

👄 ORAL (Ages 4+)

What you need:

Digital thermometer
Cooperative child who can keep mouth closed

Steps:

Wait 15-30 minutes after eating, drinking, or chewing gum (these affect temperature)
Clean the thermometer with soap and water
Turn it on and place the tip under the tongue, toward the back
Close mouth: Have your child close their lips around the thermometer (don’t bite down)
Wait for the beep (usually 30-60 seconds)
Read and record the temperature
Clean the thermometer

Tips:

Make sure your child breathes through their nose, not their mouth
Don’t let them talk while measuring
If they just drank something cold/hot, wait 15 minutes

Fever = ≥100.0°F (37.8°C) oral

🌡️ FOREHEAD (Temporal Artery)

What you need:

Temporal artery thermometer

Steps:

Remove hats or headbands and make sure forehead is dry (no sweat)
Turn on the thermometer
Place the sensor flat against the center of the forehead
Slide across the forehead: Move the thermometer across the forehead from one temple to the other, keeping it in contact with the skin
Some models: Also require you to touch behind the ear
Read the display immediately
Clean the sensor with alcohol wipe

Tips:

Don’t use right after your child comes in from outside (temperature can be affected by weather)
Make sure there’s no hair in the way
Follow the specific instructions for your brand—technique matters!
Practice a few times when your child is healthy to get the hang of it

Fever = ≥100.4°F (38°C) forehead

👂 EAR (Tympanic)

What you need:

Ear thermometer
Clean probe covers

Steps:

Use a fresh probe cover each time
Gently pull the ear: For children under 1 year, pull the ear straight back. For older kids, pull the ear up and back
Insert gently: Point the thermometer toward the opposite eye (aim toward the eardrum)
Press the button and hold until it beeps (1-2 seconds)
Remove and read the temperature
Discard the probe cover

Tips:

Ear wax can block the sensor and give a false reading
Don’t use if your child has an ear infection (it will hurt)
Take the temperature in both ears if you get an unexpected reading

Fever = ≥100.4°F (38°C) ear

💪 UNDERARM (Axillary) – Screening Only

What you need:

Digital thermometer

Steps:

Undress your child so the armpit is bare (no shirt sleeve)
Make sure the armpit is dry
Place the thermometer in the center of the armpit
Hold the arm down snugly against the body
Wait for the beep (usually 1-2 minutes—longer than other methods)
Read and record

Tips:

This method is least accurate but easiest for squirmy toddlers
If you get a fever reading with underarm, confirm with rectal or forehead
Good for a quick check, but don’t rely on it for important decisions

Fever = ≥99.0°F (37.2°C) underarm

Common Mistakes to Avoid

❌ Not waiting for the beep – Removing the thermometer too early gives an inaccurate reading

❌ Using the wrong method for age – Rectal is most accurate for babies under 3 months

❌ Not cleaning the thermometer – Always clean before and after use to prevent spreading germs

❌ Taking temperature right after bath or feeding – Wait 15-30 minutes for an accurate reading

❌ Adding/subtracting degrees – Just record what the thermometer says and note the method (e.g., “100.2°F rectal”)

❌ Checking too often – Temperature naturally fluctuates throughout the day. Check every 4-6 hours unless your child’s condition changes

How to Record Temperatures

Write down:

Date and time
Temperature reading
Method used (rectal, oral, forehead, ear, underarm)
Any medicine given (what and when)
How your child is acting

Example:

“Jan 15, 8:00 PM – 101.8°F rectal – gave Tylenol – drinking well, fussy but playful”

This information is very helpful when you call your doctor.

When to Take Your Child’s Temperature

Take a temperature if your child:

Feels warm to the touch
Is acting sick (fussy, lethargic, not eating)
Has been exposed to illness
Just received vaccines (mild fever is normal for 24-48 hours)

You don’t need to check temperature if:

Your child is acting completely normal
You’re just curious (don’t wake a sleeping child to check!)

Understanding Temperature Readings

Normal Body Temperature:

Rectal: 97.9-100.3°F (36.6-37.9°C)
Oral: 97.5-99.9°F (36.4-37.7°C)
Forehead: 97.0-99.5°F (36.1-37.5°C)
Underarm: 96.6-98.6°F (35.9-37.0°C)

Remember: Everyone’s “normal” is slightly different, and temperature naturally rises in the evening.

Low-Grade Fever:

100.4-102°F – Usually from viral infections, not dangerous

High Fever:

102-104°F – Monitor closely, treat discomfort, ensure hydration

Very High Fever:

≥105°F – Call your doctor

The number matters less than how your child looks and acts.

Thermometer Care and Maintenance

Cleaning:

After each use: Wash with soap and warm water, or wipe with rubbing alcohol
Probe covers: Change after every use (for ear thermometers)
Storage: Keep in a clean, dry case

Battery Check:

Replace batteries when the display dims
Keep a spare battery on hand

When to Replace:

If readings seem consistently off
After 2-3 years of regular use
If it’s been dropped or damaged

Quick Reference: Which Method for Which Age

Under 3 months:

✅ Rectal (call doctor for ANY fever ≥100.4°F)

3 months to 3 years:

✅ Rectal (most accurate)
✅ Forehead (if done correctly)
⚠️ Underarm (screening only)

3 to 4 years:

✅ Rectal or forehead
⚠️ Oral (if child can cooperate)

4+ years:

✅ Oral
✅ Forehead
✅ Ear (if no ear infection)

Still Have Questions?

Most pediatrician offices are happy to demonstrate proper thermometer technique at your next visit. Don’t hesitate to ask—getting an accurate temperature is an important parenting skill, and practice makes perfect!

Remember: When in doubt, call your pediatrician’s nurse line. They can help you interpret the reading and decide if your child needs to be seen.