Loading page
About this tool
Convert body temperature between Celsius, Fahrenheit and Kelvin and adjust for oral, rectal, ear, forehead or armpit readings.
The Fever Temperature Converter changes a thermometer reading between Celsius, Fahrenheit and Kelvin with the exact formulas °F = °C × 9/5 + 32 and K = °C + 273.15, then compares it against the fever threshold for the site it was taken from. Because those thresholds differ — 38.0 °C (100.4 °F) rectal or ear, 37.8 °C (100.0 °F) oral, 37.2 °C (99.0 °F) armpit — the same number can mean fever at one site and not another. It is written for parents and carers translating between a thermometer, a leaflet and a doctor who uses the other scale.
Open Fever Temperature Converter on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Uses the published fever threshold for oral, rectal, ear, forehead and armpit readings instead of one number for all.
Celsius, Fahrenheit and Kelvin from a single entry, with the core-equivalent figure alongside.
Names the hypothermia and hyperpyrexia bands and when to seek urgent care rather than guessing.
A core or rectal temperature of 38.0 °C (100.4 °F) or higher is the standard definition of fever. The equivalent thresholds are about 37.8 °C (100.0 °F) taken orally and 37.2 °C (99.0 °F) under the arm, because those sites read lower than core.
Subtract 32 and multiply by 5/9. So 100.4 °F is 38.0 °C, 101.3 °F is 38.5 °C and 104 °F is 40 °C. Going the other way, multiply Celsius by 9/5 and add 32.
It is the least reliable of the common sites and typically reads about 0.5–0.8 °C below core, which is why its fever threshold is 37.2 °C rather than 38.0 °C. Use it as a screen and confirm anything borderline with an oral, ear or rectal reading.
Seek urgent care for any fever in a baby under three months, for a core temperature at or above 41 °C (105.8 °F), or at any temperature if there is a stiff neck, a rash that does not fade under pressure, difficulty breathing, a seizure, severe drowsiness or dehydration. This tool is informational and does not replace assessment by a clinician.
Add the Fever Temperature Converterwidget to your blog or website — free, responsive, no signup. Just keep the “Widget by AltFTool” credit link visible.
<iframe src="https://www.altftool.com/embed/widget/fever-temperature-converter"
title="Fever Temperature Converter — free AltFTool widget"
width="100%" height="640" style="border:0;border-radius:12px;overflow:hidden"
loading="lazy" referrerpolicy="no-referrer-when-downgrade"></iframe>
<p style="font-size:12px;margin:4px 0 0">Widget by <a href="https://www.altftool.com/tools/all/fever-temperature-converter?utm_source=embed&utm_medium=widget">AltFTool — free online tools</a></p>