Body temperature tool
Readings vary by site; the fever check is normalized to an oral-equivalent.
Enter a realistic body temperature.
For general information only - not medical advice. See when to seek care below.
In this guide
Body temperature conversion chart
Green rows are the normal range, amber is fever, red needs urgent attention. Values rounded to one decimal; oral readings, adults.
| Fahrenheit (°F) | Celsius (°C) | What it usually means |
|---|---|---|
| 95.0 | 35.0 | Hypothermia threshold (low) |
| 96.8 | 36.0 | Below average |
| 97.7 | 36.5 | Normal range (low end) |
| 98.6 | 37.0 | Classic average |
| 99.5 | 37.5 | Normal range (high end) |
| 100.0 | 37.8 | Slightly elevated |
| 100.4 | 38.0 | Fever begins |
| 101.0 | 38.3 | Low-grade fever |
| 102.0 | 38.9 | Moderate fever |
| 103.0 | 39.4 | High fever begins |
| 104.0 | 40.0 | High fever |
| 105.0 | 40.6 | Very high - call a doctor |
| 106.0 | 41.1 | Hyperpyrexia - emergency |
What counts as a fever?
For adults and older children, a fever is generally an oral reading of 38 °C (100.4 °F) or higher. The threshold shifts with where you measure, which is why this tool normalizes every reading to an oral-equivalent before deciding.
| Site | Fever starts around | Notes |
|---|---|---|
| Rectal / Ear | 38.0 °C (100.4 °F) | Closest to core temperature |
| Mouth (oral) | 37.8 °C (100.0 °F) | Common everyday method |
| Forehead | 37.8 °C (100.0 °F) | Fast, non-invasive |
| Armpit | 37.2 °C (99.0 °F) | Reads lowest; least precise |
Fever stages and ranges
| Stage | Celsius | Fahrenheit |
|---|---|---|
| Normal | 36.5-37.5 °C | 97.7-99.5 °F |
| Slightly elevated | 37.6-37.9 °C | 99.6-100.3 °F |
| Low-grade fever | 38.0-38.9 °C | 100.4-102 °F |
| Moderate-high fever | 39.0-39.9 °C | 102.2-103.8 °F |
| High fever | 40.0-41.0 °C | 104-105.8 °F |
| Hyperpyrexia | over 41.0 °C | over 105.8 °F |
Why the measurement site changes the number
Your core temperature sits deep inside the body; every method only estimates it. Rectal reads highest and closest to core (standard for babies). Ear is quick but earwax or placement can skew it. Oral is convenient - wait ~15 minutes after eating or drinking. Forehead scanners are fast and touch-free. Armpit reads lowest, about 0.5 °C below oral, and is a rough screen only. Track the same person, same method, same time of day for fair comparisons.
Body temperature by age
Infants under 3 months: any rectal reading of 38 °C (100.4 °F) or higher is urgent - call a doctor. Children tolerate higher fevers and how they act matters as much as the number. Adults follow the chart above. Older adults run a lower baseline, so a small rise - or a serious infection with only a mild fever - can still be meaningful.
When to seek medical care
- An infant under 3 months with a rectal reading of 38 °C (100.4 °F) or higher
- Any fever above 40 °C (104 °F) that will not come down
- A fever with stiff neck, severe headache, rash, confusion, or trouble breathing
- A fever lasting more than three days or that keeps returning
- A reading below 35 °C (95 °F) in someone who feels unwell
- Signs of dehydration - little urine, dizziness, dry mouth
When in doubt, contact a healthcare professional. This tool informs; it does not replace medical advice.
Frequently asked questions
What is 37 °C in Fahrenheit?
37 °C equals 98.6 °F - the classic average. A healthy range runs about 36.5-37.5 °C (97.7-99.5 °F).
Is 37.5 °C a fever?
No. 37.5 °C (99.5 °F) is the top of the normal range. A fever generally starts at 38 °C (100.4 °F) for an oral reading.
What temperature is a fever?
Generally an oral reading of 100.4 °F (38 °C) or higher.
How do I convert Fahrenheit to Celsius?
Subtract 32, multiply by 5, divide by 9. For 100.4 °F: (100.4 − 32) × 5 ÷ 9 = 38 °C.
What is 39 °C in Fahrenheit?
39 °C equals 102.2 °F - a moderate-to-high fever worth watching.
Why is my armpit reading lower than my mouth reading?
Armpit readings sit farther from your core, so they read lower - often by about 0.5 °C - and are the least accurate method.
What body temperature is dangerous?
A fever above 40 °C (104 °F) that will not come down, or any reading above 41 °C (105.8 °F), is an emergency. Below 35 °C (95 °F) is hypothermia.
Is 96 °F too low?
96 °F is about 35.6 °C - a little below average but often normal daily variation, especially in the morning or in older adults. Seek advice if it drops toward 95 °F (35 °C) or the person feels unwell.
Sources: World Health Organization (WHO), U.S. CDC, NIH / MedlinePlus, and the UK NHS. Ranges reflect widely published clinical guidance.
Medical disclaimer: This tool converts temperatures and screens a reading against general ranges. A result is not a diagnosis and is not dosing or treatment advice. Fever thresholds vary by person, age, and measurement method. Seek professional care for an infant under 3 months with any fever, a temperature above 40 °C (104 °F) that will not come down, a reading below 35 °C (95 °F) with illness, or a fever with warning signs. When in doubt, contact a licensed healthcare provider.
Creator
Shakeel Muzaffar is the Founder and Editor-in-Chief of MultiCalculators.com, bringing over 15 years of experience in digital publishing, product strategy, and online tool development. He leads the platform's editorial vision, ensuring every calculator meets strict standards for accuracy, usability, and real-world value. Shakeel personally oversees content quality, formula verification workflows, and the platform's commitment to publishing tools that are genuinely useful for students, professionals, and everyday users worldwide.
Areas of Expertise: Editorial Leadership, Digital Publishing, Product Strategy, Online Calculators, Web Standards
