The short answer: about 37°C
Normal body temperature is approximately 37°C (98.6°F) when measured orally. It is an average, not a fixed point: your temperature is typically lowest in the early morning and highest in the late afternoon, and it varies by person, age, activity and measurement method. Modern large-scale studies put the average a little lower, around 36.6–36.8°C, but 37°C remains the figure the NHS quotes.
Body temperature conversion table
| Reading | Celsius | Fahrenheit | Meaning |
|---|---|---|---|
| Hypothermia | below 35°C | below 95°F | Medical emergency — call 999 |
| Low | 35.0–36.0°C | 95–96.8°F | Below normal; recheck and keep warm |
| Normal range | 36.1–37.2°C | 97–99°F | Typical healthy range |
| Average | 37°C | 98.6°F | Textbook normal body temperature |
| Low-grade fever | 37.3–37.9°C | 99.1–100.2°F | Elevated; NHS inform counts 37.8°C+ as fever |
| Fever | 38°C and above | 100.4°F and above | Fever — rest, fluids, monitor |
| High fever | 39–40°C | 102.2–104°F | Seek medical advice, especially for children |
| Dangerous | above 41.1°C | above 106°F | Hyperpyrexia — urgent medical attention |
Converting between °C and °F
To convert Fahrenheit to Celsius: °C = (°F − 32) × 5/9. So 98.6°F is (98.6 − 32) × 5/9 = 37°C, and a fever of 100.4°F is (100.4 − 32) × 5/9 = 38°C. Going the other way: °F = °C × 9/5 + 32. The Fahrenheit to Celsius converter does any value instantly.
Why readings differ
A rectal reading runs about 0.3–0.6°C higher than an oral one, and an armpit reading about 0.3–0.6°C lower — which is why two thermometers can disagree on the same person. Hot drinks, exercise and ovulation also raise the reading, and children run slightly warmer than adults. If a reading looks wrong, retake it after 15 minutes at rest, and compare like with like.
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