Body Temperature Converter
Convert body temperature between Fahrenheit and Celsius with clinical range interpretation including normal, fever, and hypothermia zones.
Type a body temperature in either field — the other updates instantly with clinical interpretation.
Fever threshold: 100.4°F (38°C)
High fever: above 103°F (39.4°C)
Understanding Body Temperature
Normal human body temperature is not a single fixed number but rather a range that varies based on the measurement method, time of day, age, and individual differences. The commonly cited “normal” temperature of 98.6°F (37°C) was established in 1851 by the German physician Carl Reinhold August Wunderlich, who averaged millions of readings from 25,000 patients. More recent studies suggest the average is slightly lower, around 97.9°F (36.6°C).
Conversion Formulas:
- Fahrenheit to Celsius:
°C = (°F - 32) × 5/9 - Celsius to Fahrenheit:
°F = (°C × 9/5) + 32
Clinical Temperature Ranges (Oral Measurement):
| Range | Fahrenheit | Celsius | Interpretation |
|---|---|---|---|
| Severe hypothermia | Below 86°F | Below 30°C | Medical emergency |
| Mild hypothermia | 86-95°F | 30-35°C | Seek medical attention |
| Below normal | 95-97.7°F | 35-36.5°C | Slightly cool but usually harmless |
| Normal range | 97.7-99.5°F | 36.5-37.5°C | Healthy body temperature |
| Low-grade fever | 99.5-100.4°F | 37.5-38°C | Mild elevation, monitor |
| Fever | 100.4-103°F | 38-39.4°C | Likely infection, consider medication |
| High fever | 103-104°F | 39.4-40°C | Seek medical advice |
| Hyperthermia | Above 104°F | Above 40°C | Medical emergency, call doctor immediately |
Temperature Variation by Measurement Site:
Different measurement locations give slightly different readings. Here are the typical offsets compared to oral temperature:
- Rectal: Add 0.5-1°F (0.3-0.6°C) higher than oral
- Ear (tympanic): Very close to oral, within 0.3°F (0.2°C)
- Armpit (axillary): Subtract 0.5-1°F (0.3-0.6°C) lower than oral
- Forehead (temporal): Similar to oral, within 0.5°F (0.3°C)
Practical Examples:
- A reading of 101°F orally equals 38.3°C, indicating a moderate fever.
- A child with an armpit reading of 99.5°F (37.5°C) effectively has an oral-equivalent temperature of about 100-100.5°F (37.8-38°C), which is a low-grade fever.
- An ear thermometer reading of 100.4°F (38°C) is the standard threshold most doctors use to define a fever.
Tips:
- Body temperature is lowest in the early morning (around 4-6 AM) and highest in the late afternoon (4-6 PM).
- Exercise, hot drinks, and heavy clothing can temporarily raise readings.
- In children under 3 months, any temperature of 100.4°F (38°C) or above warrants an immediate call to the pediatrician.
- Digital thermometers are more accurate and safer than older mercury glass thermometers.
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