Why does the US still use Fahrenheit?

Mostly historical inertia. The US legally made metric the "preferred" system in 1975 but never made it mandatory for everyday use. Fahrenheit also gives slightly finer gradation than Celsius for weather (the 100 °F scale covers the human comfort zone), which users argue is a benefit.

What’s the difference between Kelvin and "degrees Kelvin"?

None, but the name is "kelvin", not "degrees Kelvin". Since Kelvin is an absolute scale (0 K = absolute zero), the word "degree" isn’t used: you say "300 kelvin" or "300 K", not "300 °K". The degree symbol was officially removed in 1967.

Are there other temperature scales?

Yes. Rankine (°R) is the absolute Fahrenheit scale (0 °R = absolute zero, 1 °R = 1 °F in size), used in US engineering. Réaumur (°Ré), Delisle (°D) and Newton (°N) are historical and rarely used today. The calculator focuses on the three practical scales.

Can temperature go below absolute zero?

In classical thermodynamics: no. Absolute zero (0 K) corresponds to minimum thermal energy. In quantum systems, "negative absolute temperature" can be defined in exotic states, paradoxically interpreted as "hotter than infinity". For everyday use, the scale stops at 0 K.

/temperatur

Temperature Converter - Celsius, Fahrenheit & Kelvin

Convert temperatures between Celsius, Fahrenheit, and Kelvin instantly and locally.

Celsius (°C)

Fahrenheit (°F)

Kelvin (K)

Quick Reference

Phenomenon	Celsius (°C)	Fahrenheit (°F)	Kelvin (K)
Absolute zero	-273.15	-459.67	0
Water freezes	0	32	273.15
Room temperature	20	68	293.15
Body temperature	37	98.6	310.15
Water boils	100	212	373.15

How the temperature formulas work

The Celsius, Fahrenheit, and Kelvin temperature scales are mathematically related. Celsius and Kelvin share the same scale intervals but have different starting points (Kelvin starts at absolute zero). Fahrenheit uses both a different unit size and starting point.

Celsius ↔ Fahrenheit: °F = (°C × 9/5) + 32 | °C = (°F - 32) × 5/9
Celsius ↔ Kelvin: K = °C + 273.15 | °C = K - 273.15
Fahrenheit ↔ Kelvin: K = (°F - 32) × 5/9 + 273.15

About this tool

Temperature is measured in three main scales: Celsius (°C), Fahrenheit (°F) and Kelvin (K). Celsius is standard in Norway and most of the world outside the US; Fahrenheit is still used in the US and a couple of Caribbean countries; Kelvin is the SI unit used in science and engineering. Conversions are linear: F = C × 9/5 + 32, K = C + 273.15. This tool converts between all three simultaneously, enter a value in one scale and the others update in real time. Useful for recipes, travel, weather and physics problems. All calculations happen locally in your browser.

How to use it

Enter the desired temperature in whichever field suits you (Celsius, Fahrenheit or Kelvin).
The two other fields update automatically in real time.
Negative values are supported (e.g. −40 °C is also −40 °F, the only intersection point).
Kelvin cannot be negative; absolute zero is 0 K = −273.15 °C = −459.67 °F.
Use decimal comma or period, both are parsed correctly.

Examples

Body temperature

Input37 °C

Output98.6 °F = 310.15 K

Normal body temperature. 38 °C = 100.4 °F is usually considered fever.

Freezing point of water

Input0 °C

Output32 °F = 273.15 K

The reference point Celsius is built around. The triple point of water (0.01 °C) sits just above.

Oven temperature

Input200 °C

Output392 °F = 473.15 K

Common recipe temperature. American recipes often use 400 °F ≈ 204 °C.

Common use cases

Following American recipes without doing mental math.
Checking travel temperatures for trips to Florida, China or Morocco.
Calibrating sensors, lab equipment or 3D-printer nozzles (K used in physics).
Converting weather forecasts from foreign sites.
Physics problems: enthalpy and reaction calculations require Kelvin.
Comparing body temperature between thermometers with different scales.

Frequently asked questions

Why does the US still use Fahrenheit?: Mostly historical inertia. The US legally made metric the "preferred" system in 1975 but never made it mandatory for everyday use. Fahrenheit also gives slightly finer gradation than Celsius for weather (the 100 °F scale covers the human comfort zone), which users argue is a benefit.
What’s the difference between Kelvin and "degrees Kelvin"?: None, but the name is "kelvin", not "degrees Kelvin". Since Kelvin is an absolute scale (0 K = absolute zero), the word "degree" isn’t used: you say "300 kelvin" or "300 K", not "300 °K". The degree symbol was officially removed in 1967.
Are there other temperature scales?: Yes. Rankine (°R) is the absolute Fahrenheit scale (0 °R = absolute zero, 1 °R = 1 °F in size), used in US engineering. Réaumur (°Ré), Delisle (°D) and Newton (°N) are historical and rarely used today. The calculator focuses on the three practical scales.
Can temperature go below absolute zero?: In classical thermodynamics: no. Absolute zero (0 K) corresponds to minimum thermal energy. In quantum systems, "negative absolute temperature" can be defined in exotic states, paradoxically interpreted as "hotter than infinity". For everyday use, the scale stops at 0 K.

Technical background

The three linear formulas: (1) °F = °C × 9/5 + 32; (2) K = °C + 273.15; (3) °C = (°F − 32) × 5/9. History of the scales: Anders Celsius (1701–1744) originally set water’s boiling point to 0 and freezing point to 100, the reverse of today. Daniel Fahrenheit (1686–1736) built his scale on three points: a brine solution (0 °F), freezing (32 °F) and human body (originally 96 °F). William Thomson (Lord Kelvin) proposed the absolute scale in 1848. SI redefined the kelvin in 2019 based on Boltzmann’s constant k = 1.380 649 × 10⁻²³ J/K, without reference to water’s triple point.