Temperature Unit Converter

One reading, four temperature scales

Enter a value in Celsius (°C), Fahrenheit (°F), Kelvin (K), or Rankine (°R), then read the equivalent on all four scales. Kelvin uses K without a degree sign; Rankine is written here as °R. Réaumur is not included. The converter works from the value and unit you select, so the selected source unit matters as much as the number.

Celsius and Fahrenheit use different zero points and step sizes. Kelvin starts at absolute zero and has the same step size as Celsius; Rankine also starts at absolute zero and uses Fahrenheit-sized steps. For example, 0 °C equals 32 °F and 273.15 K. The National Institute of Standards and Technology (NIST) gives the exact Celsius, Fahrenheit, and kelvin relationships and defines the kelvin as the SI unit of thermodynamic temperature. NIST’s temperature reference supports those relationships.

Why the conversion includes both a scale and an offset

To convert a temperature reading from Celsius, use these relationships:

For the reverse direction, first convert the selected scale to Celsius, then derive the other results: °C = (°F − 32) × 5/9; °C = K − 273.15; and °C = (°R − 491.67) × 5/9. NIST confirms the Celsius/Fahrenheit/kelvin equations; the Rankine relationship follows from Rankine’s Fahrenheit-sized interval and absolute-zero origin, tabulated in NIST Guide to the SI, Appendix B.9.

Temperature readings are not temperature changes

These equations convert a point reading. If something warms by 10 °C, its temperature change is 18 °F; it is not a reading conversion and does not receive the +32 offset. This distinction matters when a source describes a rise, drop, or interval rather than the temperature itself.

Convert and check a value

1. Enter the number

   Type a positive, negative, or decimal value. A blank or unrecognized input does not produce a conversion result.

2. Choose the source scale

   Select °C, °F, K, or °R to tell the converter what the entered number means. A wrong unit can produce plausible-looking but unrelated equivalents.

3. Set displayed precision

   Choose the number of decimal places for the results. The displayed precision changes rounding only; it does not add measurement accuracy.

4. Read or copy an equivalent

   All four scales appear together. Copy a displayed number as needed, keeping its unit with it. Selecting a result can also make that scale and value the new input for a reverse check.

As a reproducible kitchen example, 350 °F converts to about 176.7 °C when shown to one decimal place. The exact conversion is (350 − 32) × 5/9 = 176.666… °C; the last displayed digit is rounded.

Common conversion questions

Use precision that matches the source

Rounding controls how many digits are displayed, not how accurately the original temperature was measured. Keep the source instrument uncertainty and significant digits in mind when reusing a result. For laboratory, engineering, or compliance records, follow the applicable measurement procedure and retain units with values.

The conversion is a calculation only. It does not read a thermometer, weather service, or other measurement source, and it does not validate the entered value against a physical or safety threshold.