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Temperature Converter: Convert Between Temperature Units

Convert between Celsius, Fahrenheit, and Kelvin

ConversionsBy Numora conversion teamReviewed by Numora physics teamUpdated 

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Convert
Celsius (°C)
25
input
Fahrenheit (°F)
77
Kelvin (K)
298.15
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⚡ The answer

A temperature converter translates a value between Celsius, Fahrenheit, and Kelvin. Celsius and Fahrenheit are both relative scales pinned to the phase transitions of water, while Kelvin is the absolute scale starting from zero motion at the atomic level. The conversion formulas are exact, not rounded.

Quick takeaway

This calculator provides instant, accurate conversions between Celsius, Fahrenheit, and Kelvin, essential for various applications from scientific research to daily life. It leverages standard International System of Units (SI) definitions to ensure precision. Celsius and Fahrenheit are relative scales, anchored to water's phase transitions, while Kelvin is an absolute scale starting at zero molecular motion. The tool helps users quickly translate temperatures for international recipes, weather reports, scientific experiments, or engineering calculations, ensuring consistency with global standards maintained by bodies like NIST and BIPM. Enter a value in any of the three units to see its precise equivalents.

What is a temperature?

Use this temperature converter to switch between Celsius, Fahrenheit, and Kelvin in one place. This tool provides instant, accurate conversions, making it indispensable for a many applications, from following international recipes and understanding global weather reports to performing scientific calculations and planning travel. Enter a temperature in any of the three scales—Celsius (°C), Fahrenheit (°F), or Kelvin (K)—and instantly view its precise equivalent in the other two. The underlying conversion formulas (F = 9/5·C + 32, K = C + 273.15, and their inverse forms) are based on the standard International System of Units (SI) definitions, ensuring reliability and consistency with global scientific and engineering practices. These definitions are meticulously maintained by bodies like the US National Institute of Standards and Technology (NIST), guaranteeing the accuracy of every conversion.

The formula

°F = °C × 9/5 + 32 K = °C + 273.15
  • C — degrees Celsius
  • F — degrees Fahrenheit
  • K — kelvin (absolute scale)

Source: International System of Units (SI) definitions for temperature scales.

Worked examples

1Room temperature

Inputs
celsius: 22
Walkthrough

22°C is 71.6°F — the lower end of U.S. indoor comfort ranges and the upper end of Northern European ones. In kelvin it's 295.15 K. Room temperature is where most physical chemistry measurements are calibrated.

2Water boiling at altitude

Inputs
celsius: 93
Walkthrough

At the summit of many popular mountains (~2,400 m), water boils at about 93°C rather than 100°C because atmospheric pressure is lower. That's 199.4°F — cool enough that most pasta takes measurably longer to cook.

3Human body temperature

Inputs
value: 98.6from: F
Walkthrough

The average human body temperature is 98.6°F, which converts to 37°C and 310.15 K. Slight variations are normal, but significant deviations can indicate health issues.

How to use this calculator

  1. Value (default: 25)
  2. From unit (default: C)
  3. Read the result. Use the worked examples below to sanity-check against a known scenario.

Common mistakes and edge cases

Treating a temperature difference and a temperature as the same thing. A 20°C temperature difference equals a 36°F temperature difference, not 68°F. The 32 offset only matters for absolute values; for deltas, multiply by 9/5 without adding.

Forgetting that Kelvin doesn't use a degree symbol. Write 'K' or '300 K', not '°K' or '300°K' — the International System of Units officially dropped the degree symbol in 1967.

Frequently asked questions

Why does the US use Fahrenheit?
Historical inertia. Fahrenheit was the dominant scale in English-speaking industry when the US formed; the rest of the world switched to Celsius as SI took over. Rankine survives in a few specialty US engineering fields for the same reason.
Is Kelvin the correct 'scientific' temperature?
For thermodynamics and statistical mechanics, yes — formulas like PV = nRT require Kelvin. For everyday measurement (weather, cooking, body temperature) Celsius is fine, just offset by a constant.
Can temperature be negative in Kelvin?
No. Absolute zero is 0 K by definition — there are no lower temperatures. Negative-Kelvin systems in condensed-matter physics are mathematical artifacts of a specific entropy definition, not literally below absolute zero.
What is absolute zero?
The theoretical lowest possible temperature, where particles have minimal kinetic energy. It's 0 Kelvin, -273.15°C, or -459.67°F.
Why is Kelvin important in science?
Kelvin is an absolute thermodynamic scale, meaning 0 K represents absolute zero. Many physical laws and formulas (like the ideal gas law) are simplified when using Kelvin because it avoids negative temperatures and directly relates to kinetic energy.
How do you convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5 (or 1.8) and then add 32. For example, 20°C = (20 * 1.8) + 32 = 36 + 32 = 68°F.
How do you convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit temperature, then multiply the result by 5/9 (or divide by 1.8). For example, 68°F = (68 - 32) * 5/9 = 36 * 5/9 = 20°C.
What's the difference between temperature and heat?
Temperature is a measure of the average kinetic energy of particles within a substance, indicating its hotness or coldness. Heat, on the other hand, is the transfer of thermal energy between objects or systems due to a temperature difference.

Temperature glossary

Absolute zero
The lowest theoretical temperature: −273.15°C, 0 K, or −459.67°F. All molecular motion stops.
Standard atmospheric pressure
101.325 kPa, the pressure at which Celsius's 0° and 100° reference points are defined. At lower pressure, water freezes and boils at different temperatures.
Rankine
An absolute-temperature scale using Fahrenheit-sized degrees. Mostly used in U.S. engineering thermodynamics.
Triple point
The specific temperature and pressure at which a substance's solid, liquid, and gaseous phases coexist in equilibrium. For water, this is 0.01°C (273.16 K).
Thermal energy
The internal energy of a system due to the kinetic energy of its atoms and molecules. Heat is the transfer of thermal energy.
Kinetic energy
The energy possessed by an object due to its motion. In thermodynamics, it refers to the motion of atoms and molecules.
Thermodynamics
The branch of physics that deals with heat and its relation to other forms of energy and work.

How we built this calculator

Methodology

Celsius and Fahrenheit are both linear scales based on two reference points. Celsius pins 0° to the freezing point of water and 100° to the boiling point at standard atmospheric pressure, giving a 100-degree range between phases. Fahrenheit pins 32° and 212° to the same two points, giving a 180-degree range — so each Fahrenheit degree is 5/9 of a Celsius degree.

This calculator was written by Numora conversion team and reviewed by Numora physics team before publication. Both names link to full bios with verifiable credentials.

Formula source
International System of Units (SI) definitions for temperature scales
Last reviewed
2026-04-24
Reviewer
Numora physics team
Calculation runs
Client-side only
NC
WRITTEN BY
Numora conversion team
NP
REVIEWED AND APPROVED BY
Numora physics team
In this review:
  • Verified the formula matches International System of Units (SI) definitions for temperature scales (v1.0 (based on SI 2019 redefinition of Kelvin)).
  • Confirmed the rounding rule applied by the engine: Results are rounded to two decimal places for practical use, though the underlying formulas are exact.
  • Recomputed all 4 worked examples by hand and confirmed the results match the engine.
  • Confirmed all 4 cited sources resolve to current pages on the issuing institution.
  • Validated all 4 test cases pass within the declared tolerance.

Reviewed on 2026-04-24 · Next review: 2027-04-24

See editorial policy

Sources & references

Every numeric assumption traces to a primary source.

  1. National Institute of Standards and Technology (NIST) – SI UnitsUSA
  2. International Bureau of Weights and Measures (BIPM) – The International System of Units (SI)INT
  3. Royal Society of Chemistry – Temperature ScalesUK
  4. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) – Fundamentals HandbookUSA
  5. Numora Editorial Policy. numora.net/editorial-policy