Body Temperature in Celsius and Fahrenheit

4 min read•June 1, 2025•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

Normal human body temperature is approximately 37°C (98.6°F), but the healthy range is broader: 36.1–37.2°C (97–99°F) for most adults. A fever is generally defined as a temperature at or above 38°C (100.4°F). These clinical thresholds differ slightly between countries because the US uses Fahrenheit and most of the world uses Celsius.

Converting a thermometer reading between Celsius and Fahrenheit is a common need when traveling, when your thermometer uses a different scale than your medical reference, or when comparing temperatures with a doctor in a different country. The formula is the same: °F = (°C × 1.8) + 32.

Body Temperature Reference

   °C     °F    Clinical interpretation
──────   ─────  ────────────────────────────────
   35.0   95.0  Mild hypothermia threshold
   36.0   96.8  Low normal range
   36.1   97.0  Low end of normal (oral)
   36.5   97.7  Normal
   36.8   98.2  Typical average (oral)
   37.0   98.6  Classic 'normal' body temp
   37.2   99.0  High end of normal
   37.5   99.5  Slightly elevated / low-grade fever
   38.0  100.4  Fever threshold (WHO definition)
   38.5  101.3  Moderate fever
   39.0  102.2  Moderate-high fever
   39.5  103.1  High fever
   40.0  104.0  High fever — seek medical care
   41.0  105.8  Very high fever — emergency
   42.0  107.6  Extremely dangerous

Measurement Method Differences

Body temperature varies by where it is measured. Rectal temperature is the most accurate and runs about 0.3–0.6°C (0.5–1°F) higher than oral. Oral (under the tongue) is the standard reference for most clinical thresholds. Axillary (armpit) runs about 0.3–0.6°C lower than oral. Ear (tympanic) and forehead (temporal) readings are convenient but less precise.

The '37°C = 98.6°F' value was established in the 19th century by German physician Carl Wunderlich from measurements on about 25,000 patients. Modern studies suggest the average oral temperature for healthy adults is closer to 36.6°C (97.9°F) — slightly lower than the classical 37°C figure.

Quick Tips

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37°C = 98.6°F — the classic normal reference, though 36.5–37°C is a more accurate typical range.
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38°C = 100.4°F — the internationally recognized fever threshold.
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36°C to 37.5°C (96.8°F to 99.5°F) is the normal range for most adults.
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If your thermometer reads in °C and you need °F: multiply by 1.8 and add 32.
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If your thermometer reads in °F and you need °C: subtract 32 and multiply by 5/9.

Frequently Asked Questions

What is a normal body temperature in Fahrenheit?

Normal oral body temperature is approximately 97–99°F (36.1–37.2°C) for most adults, with 98.6°F (37°C) as the classical reference point.

At what temperature is it a fever in Celsius?

Fever is generally defined as 38°C (100.4°F) or above. Between 37.5°C and 38°C (99.5°F–100.4°F) is considered a low-grade fever or elevated temperature.