About the Temperature Converter
A temperature converter translates between the four common scales: Celsius, Fahrenheit, Kelvin, and Rankine. Three are linear scales (constant offset between zero and equal-degree intervals); they differ only in where zero is placed and how large a degree is. Conversions are quick on paper but easy to get wrong under pressure — confusing the formula for converting C → F with F → C, for example, is one of the most common bugs in code that handles temperature.
This converter handles all four scales bidirectionally: edit any field and the others recompute. Useful when reading temperatures in unfamiliar units (US weather forecasts in Fahrenheit, scientific papers in Kelvin) or when writing software that needs to display temperature in the user's locale.
The four scales explained
Celsius sets 0°C at the freezing point of water and 100°C at the boiling point at standard pressure. Fahrenheit places 32°F at freezing and 212°F at boiling, giving a finer-grained scale (180 degrees between freezing and boiling versus Celsius's 100). Kelvin uses the same degree size as Celsius but with 0 K at absolute zero — there are no negative kelvins. Rankine does the same trick with the Fahrenheit degree, putting 0°R at absolute zero. Kelvin is the SI unit and is universal in science; Rankine survives mostly in legacy US engineering contexts.
The classic conversion formulas
C → F: F = C × 9/5 + 32. F → C: C = (F − 32) × 5/9. C → K: K = C + 273.15. F → R: R = F + 459.67. The mistake people make most often is forgetting that the difference between C and F includes the 32-degree offset; converting a temperature difference (delta-T) is different from converting an absolute temperature.
How to use the Temperature Converter
Enter a value in any scale
The other three scales recompute instantly.
Read all four
Celsius, Fahrenheit, Kelvin, and Rankine appear side by side.
Worked examples
Example 1
Input: 0°C
Result: 32°F · 273.15 K · 491.67°R
The freezing point of water.
Example 2
Input: 100°F
Result: 37.78°C · 310.93 K · 559.67°R
A typical body-temperature-range example.
Example 3
Input: −40°C
Result: −40°F
The single point where Celsius and Fahrenheit numerically agree.
Real-world use cases
- Reading US weather forecasts when you think in Celsius (or vice versa).
- Cooking with recipes in unfamiliar temperature units.
- Cross-checking scientific results between Kelvin and Celsius.
- Calibrating instruments that report in one scale when the spec is in another.
Tips & common mistakes
- For rough mental conversion C → F, double C and add 30 (close but not exact: 20°C ≈ 70°F). For F → C, subtract 30 and halve.
- −40 is the only number that reads the same in Celsius and Fahrenheit. Useful trivia, occasionally useful sanity check.
- When converting temperature differences (rate of change), drop the 32 and the 273.15 offsets — they apply only to absolute temperatures.
Frequently asked questions
Why does science use Kelvin?
It starts at absolute zero, which makes physics formulas (ideal gas law, Stefan-Boltzmann, etc.) simpler — no negative temperatures, no offsets in the equations.
Is there a temperature below absolute zero?
Not in the conventional sense. Negative kelvins exist mathematically in certain exotic quantum systems but they are hotter than positive temperatures, not colder.
Why does the US still use Fahrenheit?
Mostly historical inertia. Daily life works fine in Fahrenheit; science and medicine in the US use Celsius and Kelvin anyway.
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Last updated: June 2026 · All processing happens locally in your browser.