-40 is a meeting point
-40° is the only temperature where Celsius and Fahrenheit read the same. It’s a handy sanity-check for conversions.
Scale crossover
Temperature Converter — Celsius, Fahrenheit, Kelvin, Rankine, Réaumur
Values
Tip: use Tab to move between fields. Values round to the selected decimals.
About
Enter a value in any field; the others update instantly using standard formulas:
- °F = °C × 9/5 + 32
- °C = (°F − 32) × 5/9
- K = °C + 273.15
- °Ra = K × 9/5 = (°C + 273.15) × 9/5
- °Ré = °C × 4/5
Both Kelvin and Rankine are absolute scales (start at absolute zero). Kelvin steps match Celsius; Rankine steps match Fahrenheit.
Understanding Temperature Scales
Temperature scales are used to measure the hotness or coldness of an object. While Celsius and Fahrenheit are the most common for everyday use, other scales like Kelvin, Rankine, and Réaumur are vital in scientific and engineering fields.
The Five Scales
- Celsius (°C): The most widely used scale, with 0°C as the freezing point and 100°C as the boiling point of water.
- Fahrenheit (°F): Predominantly used in the United States, with 32°F as the freezing point and 212°F as the boiling point of water.
- Kelvin (K): The standard unit of temperature in science. It is an absolute scale, meaning 0 K is absolute zero, the theoretical point where all molecular motion ceases. There are no degrees in Kelvin.
- Rankine (°Ra): An absolute scale similar to Kelvin, but based on the Fahrenheit degree. 0°Ra is absolute zero.
- Réaumur (°Ré): An older scale, primarily used in parts of Europe in the past. Its freezing point is 0°Ré and boiling point is 80°Ré.
Conversion Formulas
The conversion between these scales is based on a set of mathematical formulas, which this calculator uses to provide instant, accurate results. For example:
- °F = °C × 9/5 + 32
- °C = (°F − 32) × 5/9
- K = °C + 273.15
- °Ra = K × 9/5 = (°C + 273.15) × 9/5
- °Ré = °C × 4/5
All conversions in this tool are performed client-side using JavaScript, ensuring your privacy and a fast user experience.
Temperature Converter: FAQs
What are the formulas used for conversion?
Examples: °F = °C × 9/5 + 32; K = °C + 273.15; °Ra = (°C + 273.15) × 9/5; °Ré = °C × 4/5.
Is this converter private?
Yes. All calculations run locally in your browser; nothing is uploaded.
What’s the difference between Kelvin and Rankine?
Both start at absolute zero. Kelvin uses Celsius-sized degrees; Rankine uses Fahrenheit-sized degrees.
5 Fun Facts about Temperature
No “degrees” in Kelvin
Kelvin drops the degree symbol and never goes negative. Each kelvin step is identical in size to one Celsius degree.
Absolute scale
Rankine is Fahrenheit’s Kelvin
Engineers who work in Fahrenheit sometimes switch to Rankine to keep absolute temperatures positive while keeping Fahrenheit-sized increments.
Engineering habit
Réaumur was a kitchen star
Recipes and dairy makers in 18th–19th century Europe used Réaumur for fermenting cheese and brewing beer before Celsius won out.
Culinary history
Fahrenheit’s quirky zero
Daniel Fahrenheit set 0°F using a brine of ice, water, and salt—the coldest mix he could make in 1724. He pegged “96°” to approximate human body temperature.
Origin story