Fever temperature converter (°C ↔ °F)
Convert a thermometer reading between Celsius and Fahrenheit and see which band it falls in, from hypothermia to high fever, with the thresholds listed.
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Type the reading exactly as your thermometer shows it.
38 °C (100.4 °F) is the threshold most health services use to define a fever.
°F = (°C × 9/5) + 32 °F = (38.2 × 9/5) + 32 °F = 38.2 × 1.8 + 32 = 100.8 °F
| degrees Celsius | degrees Fahrenheit |
|---|---|
| 35 °C | 95.0 °F |
| 35.5 °C | 95.9 °F |
| 36 °C | 96.8 °F |
| 36.5 °C | 97.7 °F |
| 36.8 °C | 98.2 °F |
| 37 °C | 98.6 °F |
| 37.2 °C | 99.0 °F |
| 37.5 °C | 99.5 °F |
| 37.8 °C | 100.0 °F |
| 38 °C | 100.4 °F |
| 38.5 °C | 101.3 °F |
| 39 °C | 102.2 °F |
| 39.5 °C | 103.1 °F |
| 40 °C | 104.0 °F |
| 40.5 °C | 104.9 °F |
| 41 °C | 105.8 °F |
| 42 °C | 107.6 °F |
The thresholds, in both scales
A thermometer reading is only useful against a threshold, and thresholds are published in whichever scale the health service uses. Here they are side by side.
| Reading | °C | °F | Usual description |
|---|---|---|---|
| Hypothermia | below 35.0 | below 95.0 | Medical emergency |
| Normal range | 36.1–37.5 | 97.0–99.5 | Varies across the day |
| Raised / low-grade | 37.5–38.0 | 99.5–100.4 | Above normal, below the fever line |
| Fever | 38.0 and above | 100.4 and above | The standard clinical threshold |
| High fever | 39.0 and above | 102.2 and above | Worth medical advice |
| Very high fever | 40.0 and above | 104.0 and above | Urgent assessment |
The 38.0/100.4 pair is not a coincidence of rounding: 38 °C converts to exactly 100.4 °F, which is why both numbers appear in guidance worldwide.
"Normal" is a range, not 37
The 37 °C figure comes from Carl Wunderlich's 1868 study of around 25,000 patients, and the 98.6 °F everyone quotes is simply that round Celsius number converted. Modern studies consistently find a lower average, around 36.6 °C, and a genuine daily rhythm: body temperature is at its lowest in the early hours of the morning and peaks in the late afternoon or early evening, with a swing of half a degree Celsius or more.
That means one reading is a snapshot. A 37.4 °C at 6 pm and a 37.4 °C at 4 am are quite different observations.
Where you measure changes the number
- Rectal — the reference standard, typically 0.3–0.6 °C above oral
- Tympanic (ear) — close to rectal when placed correctly, easily wrong when not
- Oral — the basis of most published thresholds; affected by drinking and breathing through the mouth
- Temporal (forehead) — convenient, sensitive to sweat, draughts and recent sun exposure
- Axillary (armpit) — typically 0.3–0.6 °C below oral, and the least reliable
Compare like with like. A trend measured the same way at the same time of day tells you far more than a single number from a different site.
When the number is not the point
Fever height correlates poorly with how serious an illness is. The signs that matter more than the reading: any fever at all in an infant under three months; a stiff neck, a rash that does not fade under pressure, difficulty breathing, confusion or unusual drowsiness; a fever lasting more than three days; or dehydration. Any of those warrants medical attention whatever the thermometer says. This page converts units and lists published thresholds — it does not diagnose anything.
Nothing here is recorded
Health readings are exactly the sort of thing that should not be typed into a website that uploads them. This one cannot: the conversion is arithmetic running inside the page, there is no server behind it, and there are no cookies or analytics. Turn off your network connection and the tool works identically — which is the simplest way to verify the claim.
Questions
What temperature counts as a fever?
38.0 °C, which is 100.4 °F, is the threshold nearly every health service uses. Between 37.5 and 38 °C is usually described as a raised or low-grade temperature.
Is 37 °C really "normal"?
It is an average, published in 1868 and steadily revised down since. A healthy adult ranges roughly 36.1–37.5 °C across the day, lowest in the early morning and highest in the late afternoon.
Does the measurement site change the reading?
Substantially. Rectal and ear readings run around 0.3–0.6 °C higher than oral, and armpit readings around 0.3–0.6 °C lower. Thresholds are usually quoted for oral or tympanic measurement.
Should I use this to decide about medical care?
No. This is a unit converter with the common thresholds annotated, not a diagnostic tool. Any fever in an infant under three months, or any high fever with confusion, stiff neck, rash or breathing difficulty, needs urgent medical attention regardless of the number.
Is my family's health data stored?
Nothing is stored and nothing is transmitted. The page has no server component; the conversion is arithmetic running in your browser.