How to Convert Temperatures Online
Enter a temperature value in any of the four input fields — Celsius (°C), Fahrenheit (°F), Kelvin (K), or Rankine (°R) — and all other scales update instantly. There is no submit button; conversions happen in real time as you type. The converter handles negative values, decimals, and the full range of each scale correctly.
The four temperature scales serve different purposes: Celsius is the global standard for everyday weather and cooking, Fahrenheit is used in the United States for weather and body temperature, Kelvin is the SI unit used in physics and chemistry (0 K = absolute zero), and Rankine is an absolute scale used in some engineering thermodynamic calculations. The formulas are displayed alongside results so you can verify the math or use them in your own code.
Why Use This Free Temperature Converter?
- All four temperature scales in one tool — Celsius, Fahrenheit, Kelvin, and Rankine
- Real-time conversion as you type — no button press needed
- Shows conversion formulas so you can learn and verify the math
- Handles negative values and absolute zero correctly
- 100% browser-based — no data is sent to any server
- Clean interface optimized for quick lookups — type a number, get all conversions instantly
Frequently Asked Questions
How do I convert Celsius to Fahrenheit?
The formula is: °F = (°C x 9/5) + 32. For example, 37°C (normal body temperature) is (37 x 9/5) + 32 = 98.6°F. To convert the other way, use: °C = (°F - 32) x 5/9. The two scales intersect at -40° — that is, -40°C equals -40°F exactly. The Fahrenheit scale was defined by Daniel Gabriel Fahrenheit in 1724, with 32°F as the freezing point of water and 212°F as the boiling point.
What is 37°C in Fahrenheit?
37°C equals 98.6°F. This is the commonly cited average human body temperature, established by Carl Reinhold August Wunderlich in 1851. Modern studies suggest the actual average is slightly lower, around 36.6°C (97.9°F), and varies by individual, time of day, and measurement site. A fever is generally defined as a body temperature above 38°C (100.4°F).
What is absolute zero?
Absolute zero is 0 K (Kelvin) or -273.15°C or -459.67°F. It is the lowest possible temperature — the point at which atoms have minimal thermal motion. Absolute zero is a theoretical limit that cannot be reached in practice, though scientists have cooled substances to within billionths of a degree above it. The Kelvin scale and Rankine scale both use absolute zero as their zero point, which makes them 'absolute' temperature scales.
What is the Rankine scale and who uses it?
The Rankine scale (°R) is an absolute temperature scale based on the Fahrenheit degree interval. Like Kelvin, it starts at absolute zero (0°R = 0 K = -273.15°C = -459.67°F), but each degree Rankine is the same size as one degree Fahrenheit. It is used primarily in some American engineering fields, especially thermodynamics and combustion engineering. The conversion is: °R = °F + 459.67, or equivalently, °R = K x 9/5.
Is my data private when using this converter?
Yes. Temperature conversions are pure arithmetic performed entirely in your browser using JavaScript. No values you enter are sent to any server, stored anywhere, or logged. You can verify this by opening your browser's DevTools Network tab — no network requests occur while using the tool.
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