Celsius ↔ Kelvin Temperature Converter

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°C
K

A Guide to Temperature Scale Conversion (°C and K)

Instantly convert temperatures from Celsius to Kelvin, and vice versa. Our tool provides the precise conversion required for thermodynamic calculations, chemical kinetics, and adherence to scientific standards.

About This Temperature Converter

This calculator offers a simple, real-time conversion between the Celsius (°C) and Kelvin (K) temperature scales. While Celsius is used in daily life and many lab settings, Kelvin is the absolute temperature scale and the standard unit in many scientific equations. This tool helps bridge that gap, ensuring your data is in the correct format for accurate calculations.

How the Converter Works

The relationship between Celsius and Kelvin is a simple offset. The calculator applies the official conversion factor as you type a value into either field, instantly updating the other.

  • Celsius (°C): The metric scale where 0°C is the freezing point of water and 100°C is its boiling point at standard atmospheric pressure.
  • Kelvin (K): The SI base unit of temperature. It is an absolute scale, meaning 0 K is absolute zero—the theoretical point where all molecular motion ceases. The Kelvin scale does not use a degree symbol.

Interpreting the Results

The converted value appears automatically. If you input a Celsius temperature, the corresponding Kelvin temperature is shown, and vice versa. This is crucial for scientific work, as many fundamental equations in physics and chemistry, such as the ideal gas law (PV=nRT), require temperature to be expressed in Kelvin.

Disclaimer: This tool performs a standard mathematical conversion. The accuracy of your experimental temperature reading depends on the calibration and proper use of your thermometer or probe. For educational use only.

The Scientific Foundation: Absolute Zero

The Kelvin scale was proposed by William Thomson, Lord Kelvin, in 1848. It is based on the concept of absolute zero, the coldest possible temperature, where particles have minimal vibrational motion. The size of one unit in Kelvin is identical to the size of one degree Celsius.

The conversion formulas are straightforward:

Kelvin (K) = Celsius (°C) + 273.15

Celsius (°C) = Kelvin (K) - 273.15

The value 273.15 is the precise offset between the two scales, determined by the triple point of water.

Key Temperature Benchmarks
Phenomenon Celsius (°C) Kelvin (K)
Absolute Zero -273.15 °C 0 K
Water Freezes 0 °C 273.15 K
Human Body (Average) 37 °C 310.15 K
Water Boils (at 1 atm) 100 °C 373.15 K

Best Practices for Temperature Measurement

  • Use Calibrated Thermometers: Ensure any thermometer or temperature probe is calibrated against a known standard for accurate readings.
  • Allow for Equilibration: When measuring the temperature of a solution, allow sufficient time for the probe to reach thermal equilibrium with the liquid.
  • Proper Probe Immersion: Immerse the temperature probe deep enough into the sample to get an accurate reading, but without touching the bottom or sides of the container if it is being heated.
  • Record the Correct Unit: Always include the unit (°C or K) when recording temperatures in your lab notebook.

Conclusion: The Language of Thermodynamics

While Celsius is practical for many applications, Kelvin is the fundamental language of thermodynamics and physical chemistry. Understanding the relationship and being able to convert between these scales is a basic requirement for any scientist. This tool ensures that this simple but critical conversion is done quickly and accurately.

Final Recommendation: For any calculation involving gas laws, reaction kinetics, or thermodynamic properties (like Gibbs free energy or entropy), always convert your temperatures to Kelvin first to ensure the validity of your results.

Frequently Asked Questions

What is the formula to convert Celsius to Kelvin?

The formula is: K = °C + 273.15. You add 273.15 to the Celsius temperature to get the Kelvin equivalent.

What is the formula to convert Kelvin to Celsius?

The formula is: °C = K - 273.15. You subtract 273.15 from the Kelvin temperature to get the Celsius equivalent.

Why is 273.15 used in the conversion?

The number 273.15 represents the temperature of the triple point of water (where water can coexist as a solid, liquid, and gas) in Kelvin, minus the 0.01 degree offset. It is the precise difference between the zero points of the Celsius and Kelvin scales.

Is there a temperature where Celsius and Kelvin are the same?

No. Because there is a fixed offset of 273.15 between the two scales, their values can never be equal.

Why doesn't the Kelvin scale use the word "degrees"?

Kelvin is an absolute scale where 0 K is a true zero point (absolute zero). Scales like Celsius are relative scales defined between two points (like the freezing and boiling of water). Therefore, Kelvin is referred to by its unit name, "kelvin" (symbol K), not "degrees Kelvin."

What is absolute zero?

Absolute zero (0 K or -273.15 °C) is the lowest possible temperature. At this point, particles have the minimum possible thermal energy, according to the laws of quantum mechanics.

Can anything be colder than 0 Kelvin?

No. According to our current understanding of thermodynamics, it is impossible to reach a temperature below absolute zero.

Why is Kelvin important for scientific calculations?

Many scientific laws (like the Ideal Gas Law, PV=nRT) describe a direct proportionality to temperature. These relationships only work when using an absolute scale like Kelvin, as a zero value represents a true absence of temperature-related energy.

Is the size of a kelvin the same as a degree Celsius?

Yes. A change in temperature of 1 K is exactly equal to a change in temperature of 1 °C. This makes converting temperature *changes* or *differences* trivial.

How does Fahrenheit compare to Celsius and Kelvin?

The Fahrenheit scale has a different zero point and a different size for its degrees. The conversion is more complex: °C = (°F - 32) × 5/9.

What is the freezing point of water in Kelvin?

The freezing point of water at standard pressure is 0 °C, which is 273.15 K.

What is the boiling point of water in Kelvin?

The boiling point of water at standard pressure is 100 °C, which is 373.15 K.

Is it common to use just 273 for the conversion?

In many high school or introductory chemistry settings, 273 is used as a convenient approximation. However, for precise scientific work, the full value of 273.15 should always be used.

What is the "triple point of water"?

The triple point of water is a specific temperature and pressure (273.16 K and 611.66 pascals) at which water can exist simultaneously in solid (ice), liquid (water), and gaseous (vapor) states in stable equilibrium.

Does this calculator work for negative Celsius values?

Yes, simply enter a negative number in the Celsius field. The calculator will correctly determine the corresponding Kelvin temperature (which will always be a positive number).

Why can't I enter a negative Kelvin value?

The Kelvin scale is an absolute scale, and its zero point (0 K) is absolute zero, the lowest possible temperature. Therefore, negative Kelvin temperatures do not physically exist.

What temperature scale is used in most scientific papers?

Kelvin (K) is the standard for physical sciences, especially in thermodynamics and materials science. Celsius (°C) is still widely used in biological and environmental sciences for convenience.

How do I measure temperature accurately in a lab?

Use a calibrated digital thermometer or a properly calibrated glass thermometer. Ensure the probe is fully immersed in the substance and allow time for the reading to stabilize before recording the value.

Does the conversion factor ever change?

No, the relationship K = °C + 273.15 is a defined constant and does not change.

Who was Lord Kelvin?

William Thomson, 1st Baron Kelvin, was a prominent British mathematical physicist and engineer in the 19th century who did groundbreaking work in thermodynamics, leading to the development of the absolute temperature scale that now bears his name.

Is there a "room temperature" in Kelvin?

Standard room temperature is often considered to be around 20-25 °C. In Kelvin, this corresponds to a range of approximately 293.15 K to 298.15 K.

What is the temperature of the sun's surface in Kelvin?

The surface of the sun is approximately 5,778 K.

Is this tool appropriate for weather forecasting?

While the conversion is mathematically correct, weather forecasts are almost universally given in Celsius or Fahrenheit for public understanding. This tool is intended for scientific applications.

Who should I consult for help with thermal experiments?

For any laboratory procedure, especially those involving temperature control, consult with your lab supervisor, a senior researcher, or refer to your institution's safety protocols.

Is my data being stored?

No. All calculations are performed entirely in your browser. No data is sent to our servers, ensuring complete privacy and security.