Temperature Converter
This converter uses the defined relationships between Celsius, Fahrenheit, and Kelvin and is reviewed for calculation accuracy and clarity. Results are rounded for display where appropriate.
Convert between Celsius (°C), Fahrenheit (°F), and Kelvin (K) in any direction on one page. Enter a value, choose the source and target scale, and the tool shows the converted result, the same temperature on all three scales, the exact conversion formula for that pair, and a reference table of common temperatures. Temperature is an affine conversion — the scales have different zero points — so it is never a single multiplication.
Example result shown below. Edit the fields above and it recalculates instantly.
How It Works
The three scales measure the same physical quantity but start counting in different places and use different degree sizes. Celsius sets 0° at the freezing point of water and 100° at its boiling point. Fahrenheit puts those points at 32° and 212°, so a Fahrenheit degree is smaller (there are 180 of them between freezing and boiling versus 100 Celsius degrees — the 9/5 ratio). Kelvin uses the same degree size as Celsius but starts at absolute zero, the coldest possible temperature, which is −273.15 °C.
Because the zero points differ, every conversion has two parts: a scale factor (9/5 or 5/9) and an offset (the 32° or 273.15 shift). Getting the order right matters — for Fahrenheit to Celsius you subtract 32 first, then multiply by 5/9.
Worked Examples
Water freezes: 0 °C = 32 °F = 273.15 K.
Water boils: 100 °C = 212 °F = 373.15 K.
Body temperature: 37 °C = 98.6 °F ≈ 310.15 K.
The scales cross: −40 °C = −40 °F — the one temperature that reads the same on both.
What This Result Means
The headline is your direct conversion; the "All scales" table shows the same temperature on Celsius, Fahrenheit, and Kelvin together, which is often more useful than a single number. Kelvin has no negative values in the physical world — anything below 0 K (−273.15 °C) is colder than absolute zero and is flagged as not physically possible.
When to Use This Calculator
Use it for weather in a country that reports the other scale, cooking and oven temperatures, science and lab work (where Kelvin is standard), medical readings, and any time you need the same temperature expressed on more than one scale at once.
Limitations
- Values below absolute zero (−273.15 °C, −459.67 °F, 0 K) are shown for the math but flagged as not physically real.
- Results are displayed to a sensible precision; exact landmarks such as 0 °C = 32 °F and 100 °C = 212 °F are preserved exactly.
- This converts standard thermodynamic temperature scales; it does not handle wind-chill, heat-index, or "feels-like" adjustments, which depend on more than temperature.
Frequently Asked Questions
What is the formula for Celsius to Fahrenheit?
°F = °C × 9/5 + 32. For the reverse, °C = (°F − 32) × 5/9 — subtract 32 first, then scale.
Why is Kelvin offset by 273.15 and not 273?
Absolute zero is defined as exactly −273.15 °C, so K = °C + 273.15. The 273 shortcut is a rounding that introduces a small error.
At what temperature do Celsius and Fahrenheit read the same?
−40°. −40 °C equals −40 °F — it is the single point where the two scales cross.
Can temperature be negative in Kelvin?
No. Kelvin starts at absolute zero, so a real temperature is never below 0 K. A negative Kelvin result means the input was below absolute zero and is not physically possible.