Celsius to Kelvin Converter 2026 | Free Temperature Conversion Tool

Temperature Conversion 2026

Celsius to Kelvin Converter

Accurate temperature conversion tool for Celsius and Kelvin scales

Convert Celsius to Kelvin instantly with precise calculations. Includes bidirectional conversion and full temperature breakdowns for science, physics, chemistry, and engineering in 2026.

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🌡️ Celsius to Kelvin Converter

Professional temperature conversion for science, physics, engineering, and everyday use

✔ Accurate Conversions

Convert Celsius to Kelvin using the exact SI-defined formula: K = °C + 273.15. This is a precise, internationally standardised relationship with no approximation involved. Results are reliable for temperatures ranging from absolute zero to the surface of the sun and beyond.

✔ Bidirectional Tool

Switch seamlessly between Celsius to Kelvin and Kelvin to Celsius conversion modes. Results are also shown in Fahrenheit and Rankine so you get a complete picture of your temperature value across all four major temperature scales from a single input.

✔ Practical Applications

Essential for chemistry, physics, thermodynamics, astrophysics, and cryogenics. Kelvin is the SI base unit of temperature and is required for calculations involving gas laws, black-body radiation, and absolute temperature comparisons. One of the most important scientific conversions in 2026.

🧮 Convert Celsius to Kelvin

Select conversion direction and enter your temperature value below

Enter Temperature in Celsius (°C)

Enter the temperature in degrees Celsius to convert to Kelvin

Enter Temperature in Kelvin (K)

Enter the temperature in Kelvin to convert to Celsius (min 0 K)

Kelvin (K)

Equivalent temperature

Complete Temperature Breakdown

Celsius (°C)

Kelvin (K)

Fahrenheit (°F)

Rankine (°R)

Above Abs. Zero

0 K

Above Water Freeze

0°C

Detailed Breakdown

Understanding Celsius to Kelvin Conversion

The Celsius scale (°C) is the most widely used temperature scale in everyday life, where water freezes at 0°C and boils at 100°C at standard atmospheric pressure. The Kelvin scale (K) is the SI base unit of thermodynamic temperature, defined so that 0 K is absolute zero — the theoretical point at which all thermal motion ceases. The Kelvin scale uses the same degree interval as Celsius, making conversion between them a simple addition or subtraction of 273.15.

The offset of 273.15 comes from the fact that absolute zero (0 K) equals −273.15°C. Because both scales have identical degree increments, a temperature difference of 1°C equals a difference of 1 K. This relationship is foundational in thermodynamics, energy calculations, and heat transfer engineering, where absolute temperature in Kelvin is required for gas law equations and radiation formulas.

📌 Celsius to Kelvin Formula

Kelvin = Celsius + 273.15

Celsius = Kelvin − 273.15

Example: 100°C + 273.15 = 373.15 K (water boiling point)

Example: 0°C + 273.15 = 273.15 K (water freezing point)

📊 Temperature Scale Reference — Key Fixed Points

−273.15°C Absolute Zero (0 K)

→

0°C Water Freezes (273.15 K)

→

100°C Water Boils (373.15 K)

→

37°C Body Temp (310.15 K)

Common reference temperatures shown in Celsius with their Kelvin equivalents.

Celsius to Kelvin Conversion Table

Use this quick-reference table for common Celsius to Kelvin conversions. All values use the exact formula K = °C + 273.15 and are accurate to 2 decimal places.

Celsius (°C)	Kelvin (K)	Fahrenheit (°F)	Rankine (°R)	Reference Point
−273.15°C	0 K	−459.67°F	0°R	Absolute Zero
−196°C	77.15 K	−320.8°F	138.87°R	Liquid nitrogen
−40°C	233.15 K	−40°F	419.67°R	°C = °F crossover
0°C	273.15 K	32°F	491.67°R	Water freezing point
20°C	293.15 K	68°F	527.67°R	Room temperature
37°C	310.15 K	98.6°F	558.27°R	Human body temp
100°C	373.15 K	212°F	671.67°R	Water boiling point
500°C	773.15 K	932°F	1,391.67°R	Iron casting temp
1,000°C	1,273.15 K	1,832°F	2,291.67°R	Steel melting range
5,500°C	5,773.15 K	9,932°F	10,391.67°R	Sun surface approx

Cold Temperatures

−273.15°C0 K

−196°C77.15 K

−40°C233.15 K

0°C273.15 K

Everyday Temperatures

20°C293.15 K

37°C310.15 K

100°C373.15 K

High Temperatures

500°C773.15 K

1,000°C1,273.15 K

5,500°C5,773.15 K

How to Convert Celsius to Kelvin

Converting Celsius to Kelvin requires only a single addition step. Add 273.15 to the Celsius value to get the Kelvin equivalent. Because the two scales share the same degree size, no multiplication is needed — the scales are simply offset from each other by 273.15 degrees, the distance between absolute zero and the freezing point of water.

            📘 Step-by-Step: Convert 25°C to Kelvin
            Step 1: Identify the value — 25 degrees Celsius (typical room temperature)
Step 2: Apply the formula: 25 + 273.15 = 298.15 K
Step 3: Verify reverse: 298.15 − 273.15 = 25°C ✔

        

Reverse Conversion: Kelvin to Celsius

To convert Kelvin back to Celsius, subtract 273.15 from the Kelvin value. For example, 500 K − 273.15 = 226.85°C. This reverse conversion is used in gas pressure and thermodynamic calculations where results are produced in Kelvin by physics equations but need to be expressed in Celsius for practical engineering or scientific reporting.

⚗️ Chemistry & Gas Laws

The ideal gas law (PV = nRT) and related equations require temperature to be expressed in Kelvin. Using Celsius in these formulas produces incorrect results. Chemists convert Celsius readings from lab thermometers to Kelvin before applying gas law calculations for pressure, volume, and temperature relationships.

🔭 Astrophysics & Cosmology

Stellar temperatures, cosmic microwave background radiation, and black-body radiation calculations all use Kelvin as the standard temperature unit. The surface temperature of the Sun is approximately 5,778 K (5,505°C), while the cosmic microwave background is about 2.725 K (−270.425°C).

🧊 Cryogenics

Cryogenic science deals with extremely low temperatures near absolute zero. Liquid helium boils at 4.2 K (−268.95°C), liquid nitrogen at 77.15 K (−196°C), and liquid oxygen at 90.19 K (−182.96°C). Kelvin is the only practical scale for communicating cryogenic temperatures clearly and without ambiguity.

💡 Colour Temperature

Light bulb and display colour temperature is measured in Kelvin. A warm white LED is approximately 2,700–3,000 K, neutral white is 4,000 K, and daylight is 5,000–6,500 K. Understanding Kelvin temperature helps consumers and lighting designers choose correct light sources for residential, commercial, and photographic applications.

🏭 Industrial Thermodynamics

Thermodynamic efficiency calculations for engines, turbines, and heat pumps — including the Carnot efficiency formula — require temperatures in Kelvin. Engineers convert operating temperatures from Celsius gauges to Kelvin for accurate efficiency modelling, heat exchanger design, and thermal management in industrial processes.

🔬 Materials Science

Phase diagrams, thermal conductivity data, and material property specifications in materials science use Kelvin as the standard temperature unit. Melting points, glass transition temperatures, and superconducting critical temperatures are all expressed in Kelvin for precise scientific communication across research institutions worldwide.

✅ Key Conversion Facts — Celsius & Kelvin

0 K = −273.15°C (absolute zero — the lowest possible temperature)
273.15 K = 0°C (water freezing point at standard pressure)
373.15 K = 100°C (water boiling point at standard pressure)
310.15 K = 37°C (normal human body temperature)
293.15 K = 20°C (standard room temperature)
A temperature difference of 1°C = a difference of 1 K (same degree size)

⚠️ Common Mistakes to Avoid

Using 273 instead of 273.15: Rounding to 273 introduces a 0.15 K error — significant in precise scientific work. Always use the exact value of 273.15 unless a rough estimate is acceptable.
Negative Kelvin values: Kelvin cannot be negative — 0 K is the absolute minimum. If your conversion produces a negative Kelvin result, the input Celsius value is below −273.15°C, which is physically impossible.
Writing "°K" instead of "K": The correct symbol for Kelvin is simply K — no degree symbol. Writing °K is a common formatting error. Celsius uses °C, Fahrenheit uses °F, but Kelvin uses K alone.

Frequently Asked Questions — Celsius to Kelvin

How do you convert Celsius to Kelvin?

To convert Celsius to Kelvin, add 273.15 to the Celsius value. The formula is: K = °C + 273.15. For example, 25°C + 273.15 = 298.15 K. This works because 0 K (absolute zero) corresponds to −273.15°C, so the two scales are simply offset by that amount. The degree size is identical on both scales.

What is 0°C in Kelvin?

0°C equals 273.15 K. This is the freezing point of water at standard atmospheric pressure (101.325 kPa). It is one of the most important reference points in thermometry. On the Kelvin scale, this value is above absolute zero by exactly 273.15 degrees, reflecting the definition of the Kelvin scale.

What is absolute zero in Celsius?

Absolute zero — 0 K — equals exactly −273.15°C. It is the lowest temperature theoretically possible, the point at which all classical thermal motion stops. It has never been achieved in practice, though scientists have reached temperatures within billionths of a degree of absolute zero in laboratory experiments.

Why is Kelvin used in science instead of Celsius?

Kelvin is used in science because it is an absolute temperature scale — it starts at absolute zero with no negative values. Many scientific formulas, including the ideal gas law, Stefan-Boltzmann law, and Wien's displacement law, only produce correct results when temperature is expressed in Kelvin. Celsius, being an offset scale, introduces errors in these calculations.

Is a change of 1°C the same as a change of 1 K?

Yes. A temperature change (difference) of 1°C is exactly equal to a temperature change of 1 K. Both scales use the same degree interval — they are only shifted relative to each other by 273.15. So if a substance heats up by 10°C, it has also heated up by 10 K. This is why you can use either unit when expressing temperature differences, but must use the correct offset for absolute temperatures.

What is body temperature in Kelvin?

Normal human body temperature of 37°C equals 37 + 273.15 = 310.15 K. In clinical settings, temperature is measured and reported in Celsius (or Fahrenheit in the US), but in physiology research and biophysics calculations, body temperature is often expressed in Kelvin. A fever of 39°C = 312.15 K, and hypothermia below 35°C = below 308.15 K.

Temperature Conversion Resources

🌐 BIPM — Kelvin Definition

The International Bureau of Weights and Measures (BIPM) defines the Kelvin as the SI base unit of thermodynamic temperature. Since 2019, the Kelvin has been redefined in terms of the Boltzmann constant (k = 1.380649 × 10⁻²³ J/K), replacing the older water triple-point definition.

Visit BIPM →

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📐 NIST Temperature Reference

The US National Institute of Standards and Technology (NIST) publishes official thermometric reference data, including fixed-point temperatures on the International Temperature Scale of 1990 (ITS-90), which underpins all modern Celsius and Kelvin calibration standards.

Visit NIST →