What this calculator does
This tool converts a body-temperature reading between Fahrenheit (°F) and Celsius (°C) and tells you immediately whether the value reaches the common fever threshold of 38 °C / 100.4 °F. It is handy when a thermometer reports one scale but your guidance or records use the other.
How to use it
Pick the unit your thermometer shows — Fahrenheit or Celsius — type in the reading, and submit. You will get the converted value plus a clear banner indicating "fever" or "no fever" based on the 38 °C threshold.
The formula explained
The two scales are linearly related. To go from Fahrenheit to Celsius, subtract 32 and multiply by 5/9: $$\text{C} = \left( \text{Temp } (^{\circ}\text{F}) - 32 \right) \times \frac{5}{9}$$. To go the other way, multiply by 9/5 and add 32: $$\text{F} = \text{Temp } (^{\circ}\text{C}) \times \frac{9}{5} + 32$$. The constant 32 aligns the freezing point of water, while 9/5 (or 5/9) scales the size of one degree between the systems.
Worked example
Suppose your thermometer reads 100.4 °F. Subtract 32 to get 68.4, then multiply by 5/9: $$68.4 \times \frac{5}{9} = 38.0\ ^{\circ}\text{C}$$. Because 38.0 °C is exactly at the threshold, the calculator flags a fever. A reading of 98.6 °F gives \(\left( 98.6 - 32 \right) \times \frac{5}{9} = 37.0\ ^{\circ}\text{C}\) — a normal temperature, no fever.
FAQ
What counts as a fever? Clinically a fever is commonly defined as a body temperature of 38 °C (100.4 °F) or higher, though the exact cutoff can vary by source and measurement site.
Is the conversion exact? Yes — the formula is exact. Displayed values are rounded to two decimals for readability.
Should I rely on this for medical decisions? No. This is an educational conversion tool. Always follow professional medical advice for diagnosis and treatment.
