Temperature Converter

The formulas the converter applies

Temperature is the one quantity on this site that cannot be converted with a single multiplier, because the scales have different zero points. The widget always converts the input to Celsius first and then from Celsius to the target scale, so a Fahrenheit to Kelvin conversion is two steps joined together.

Worked examples

• 300 K to Fahrenheit: 300 − 273.15 = 26.85 °C, then 26.85 × 1.8 + 32 = 80.33 °F.
• A 350 °F oven: (350 − 32) × 5/9 = 176.67 °C, shown with two decimals because the value is over 100.
• Body temperature: 37 °C × 1.8 + 32 = 98.6 °F, and 37 + 273.15 = 310.15 K.
• 100 °F to Celsius: 68 × 5/9 = 37.7778 °C (four decimals, since the result is between 1 and 100).
• Absolute zero: 0 K is −273.15 °C and −459.67 °F; at −40 the Celsius and Fahrenheit readings coincide.

Reference points in all three scales

What the widget checks and what it does not

• Any finite number is accepted, including values below absolute zero, but those are flagged: entering −300 °C still shows the arithmetic result of −26.85 K, and a warning under the fields points out that nothing can be that cold.
• It converts temperature points, not differences. A rise of 10 °C is a rise of 18 °F, not 50 °F; to convert an interval, multiply by 1.8 (or 5/9) and skip the 32.
• Only Celsius, Fahrenheit and Kelvin are offered; Rankine (°F + 459.67), Réaumur and Delisle are not.
• Kelvin is printed without a degree sign, following SI practice since 1967.
• Values of 100 or more keep two decimals, so 310.15 K stays 310.15; smaller values keep four decimals, and trailing zeros are dropped, which is why 98.6 °F does not become 98.6000.

How the three result cards behave

Underneath the main result the widget lays out three cards, one per scale, and highlights the one matching your To selection. The card for the source scale repeats your input, so entering 100 °C shows Celsius 100, Fahrenheit 212 and Kelvin 373.15 together, which makes it easy to quote a temperature in every scale in a document. Clear the box and the cards disappear while the main result shows a dash; there is no separate error message for an empty field.

Precision in practice

The familiar 98.6 °F is itself a conversion of 37 °C, which was a rounded nineteenth-century average; modern studies put normal body temperature closer to 36.6 °C (97.9 °F). Weather forecasts are rounded to whole degrees, so converting 72 °F to 22.2222 °C does not add real information; 22 °C is the honest reading. Laboratory and cooking work can use the extra decimals the cards provide.