Temperature Converter

Convert between Celsius, Fahrenheit, and Kelvin.

Value

From

Result

°F

Common Temperature References

Freezing point of water: 0°C = 32°F = 273.15K

Boiling point of water: 100°C = 212°F = 373.15K

Body temperature: 37°C = 98.6°F = 310.15K

Frequently Asked Questions

How do I convert Celsius to Fahrenheit?

To convert C to F, multiply by 9/5 and add 32. Formula: F = (C × 9/5) + 32. For example, 100°C = (100 × 9/5) + 32 = 212°F.

What is absolute zero?

Absolute zero is -273.15°C or -459.67°F, which is the coldest possible temperature where all molecular motion stops.

How do you convert Celsius to Kelvin?

To convert C to K, simply add 273.15. Formula: K = C + 273.15. For example, 0°C = 273.15K.

Temperature is one of the few everyday measurements with no single global unit. Most of the world uses Celsius, the United States still uses Fahrenheit for weather, cooking, and body temperature, and scientists work almost exclusively in Kelvin. The temperature-converter on this page switches between the four scales in common use: Celsius (°C), Fahrenheit (°F), Kelvin (K), and Rankine (°R).

The four scales are built on different reference points. Celsius sets 0 °C at the freezing point of water and 100 °C at the boiling point, both at standard atmospheric pressure. Fahrenheit sets 32 °F at freezing and 212 °F at boiling, a 180-degree spread, so each Fahrenheit degree is smaller than a Celsius degree. Kelvin is the SI base unit of thermodynamic temperature and starts at absolute zero, the coldest possible temperature, where molecular motion stops. Rankine is the absolute-scale version of Fahrenheit, used mostly in older US engineering work. The relationship between any two scales is a linear equation because both endpoints are fixed.

The two key formulas to remember: °F = °C × 9/5 + 32, and K = °C + 273.15. Going the other way, °C = (°F − 32) × 5/9, and °R = °F + 459.67. A few reference values that come up often: 0 °C is 32 °F or 273.15 K, 25 °C is 77 °F or 298.15 K, 100 °C is 212 °F or 373.15 K, and absolute zero is −273.15 °C, 0 K, −459.67 °F, or 0 °R.

A common trap is the offset. A 1 °C change is a 1.8 °F change, not 1 °F, and a 1 K change equals a 1 °C change exactly because both are SI units on the same scale. This matters for cooking (an oven recipe in °F should not be converted by simple subtraction) and for science (a temperature of 300 K is the same step as 27 °C above 273 K). The converter handles all of these at once, so a single number populates every field at the same precision.

How to use

Type a value in any of the four fields: Celsius, Fahrenheit, Kelvin, or Rankine.
The other three scales update automatically at the same precision.
Use Kelvin or Rankine for scientific work and physics; use Celsius or Fahrenheit for daily use.
Clear the form to start a new conversion; the precision matches the digits entered.

Formula

°F = (°C × 9/5) + 32. K = °C + 273.15. °C = (°F − 32) × 5/9. °R = °F + 459.67. A 1 °C change equals a 1.8 °F change or a 1 K change.

Interpreting your results

Negative values on Kelvin or Rankine are physically impossible and indicate an input below absolute zero, which the laws of thermodynamics do not allow. Celsius and Fahrenheit can both be negative, but only below their respective zero points (0 °C is freezing water, 0 °F is colder than freezing and was originally based on a brine mixture). For body temperature, 37.0 °C is the classic normal reading and 38.0 °C is the common fever threshold; in Fahrenheit those are 98.6 °F and 100.4 °F, the value most US medical guides quote.

Frequently asked questions

What is the formula to convert Celsius to Fahrenheit?

The formula is °F = (°C × 9/5) + 32. For example, 25 °C is (25 × 1.8) + 32 = 77 °F. The 9/5 factor (or 1.8) handles the different degree size, and the +32 handles the offset between the zero points of the two scales.

Why does the US use Fahrenheit?

Fahrenheit was proposed by Daniel Gabriel Fahrenheit in 1724 and became widely adopted in the English-speaking world. Most countries moved to Celsius in the 20th century as part of metrication, but the US kept Fahrenheit for everyday use, and the Cayman Islands, Belize, and Liberia do the same. Science and medicine in the US still use Celsius for most published data.

What is absolute zero?

Absolute zero is the lowest possible temperature, where classical physics predicts that all molecular motion would stop. It is 0 K, −273.15 °C, or −459.67 °F, and it is unreachable in practice, though laboratory systems have come within a few billionths of a kelvin. The third law of thermodynamics states that it cannot be reached exactly.

Is a degree Celsius the same size as a Kelvin?

Yes, a 1 °C change equals a 1 K change exactly. The two scales differ only in their zero point: 0 K is absolute zero, while 0 °C is the freezing point of water (273.15 K above absolute zero). This is why scientific temperatures are usually given in Kelvin but temperature differences can be written in either.