Celsius to Kelvin Converter

Converting temperatures from Celsius (°C) to Kelvin (K) is straightforward and commonly used in scientific work, particularly in physics and chemistry. The Kelvin scale starts at absolute zero, making it the preferred choice for scientific measurements.

Enter Temperature in Celsius (°C)

Temperature in Kelvin (K)

Quick Conversions

Celsius to Kelvin Conversion Table

Here are the most frequently used temperature conversions from Celsius to Kelvin. This table helps you quickly reference common values without needing to perform the maths each time.

Celsius (°C)	Kelvin (K)	Description
-273.15	0	Absolute zero
-200	73.15	Cryogenic temperatures
-100	173.15	Very cold
-40	233.15	Extremely cold weather
-18	255.15	Freezer temperature
0	273.15	Water freezing point
10	283.15	Cool day
20	293.15	Room temperature
25	298.15	Comfortable temperature
37	310.15	Human body temperature
50	323.15	Hot summer day
100	373.15	Water boiling point
200	473.15	Baking temperature
500	773.15	High-temperature processes
1000	1273.15	Industrial applications

Formula and Steps

The conversion from Celsius to Kelvin uses a simple addition. Unlike Celsius to Fahrenheit, which requires multiplication and addition, this conversion only requires adding a constant value.

K = °C + 273.15

Where:

K = Temperature in Kelvin
°C = Temperature in Celsius
273.15 = Conversion constant

Step-by-Step Conversion Process

Take your temperature value in Celsius
Add 273.15 to this value
The result is your temperature in Kelvin
Note that Kelvin doesn’t use the degree symbol (°)

Worked Examples

Example 1: Room Temperature
Convert 21°C to Kelvin:
K = 21 + 273.15 = 294.15 K

Example 2: Water’s Boiling Point
Convert 100°C to Kelvin:
K = 100 + 273.15 = 373.15 K

Example 3: Negative Temperature
Convert -40°C to Kelvin:
K = -40 + 273.15 = 233.15 K

The Science Behind the Scales

Both Celsius and Kelvin are metric temperature scales with identical degree increments. What distinguishes them is their starting point.

Celsius Scale

Developed by Swedish astronomer Anders Celsius in 1742, this scale sets the freezing point of water at 0°C and the boiling point at 100°C under standard atmospheric pressure. It’s widely used across Europe and most of the world for everyday temperature measurements.

Kelvin Scale

Created by British physicist Lord Kelvin (William Thomson) in 1848, this absolute temperature scale begins at absolute zero—the theoretical temperature where all molecular motion ceases. One kelvin equals one degree Celsius in magnitude, but the scale starts at -273.15°C, which becomes 0 K.

Why Scientists Prefer Kelvin

The Kelvin scale avoids negative numbers, which simplifies many scientific equations. It’s the SI base unit for thermodynamic temperature and is essential in fields like:

Quantum physics and low-temperature research
Thermodynamics and heat transfer studies
Chemistry and reaction rate calculations
Astronomy and stellar temperature measurements
Engineering and materials science

Temperature Units Conversions

If you need to convert between other temperature scales, here are the key relationships:

From	To	Formula
Celsius	Kelvin	K = °C + 273.15
Kelvin	Celsius	°C = K – 273.15
Celsius	Fahrenheit	°F = (°C × 9/5) + 32
Kelvin	Fahrenheit	°F = (K – 273.15) × 9/5 + 32
Fahrenheit	Celsius	°C = (°F – 32) × 5/9
Fahrenheit	Kelvin	K = (°F – 32) × 5/9 + 273.15

Common Usage Scenarios

Laboratory Work: When conducting experiments that involve gas laws, chemical reactions, or thermodynamic processes, measurements are typically recorded in Kelvin. This eliminates complications from negative values and maintains consistency with SI units.

Climate Science: Whilst weather forecasts use Celsius for public communication, climate models and atmospheric science often work in Kelvin for computational accuracy and compatibility with physical equations.

Space Exploration: NASA and other space agencies primarily use Kelvin when measuring temperatures in space, from the cosmic microwave background (2.7 K) to stellar surfaces (thousands of kelvins).

Cryogenics: The study of materials at extremely low temperatures relies exclusively on Kelvin. Liquid nitrogen, for instance, has a boiling point of 77 K (-196°C).

FAQs

Why do we add 273.15 when converting Celsius to Kelvin?

The number 273.15 represents the difference between absolute zero and water’s freezing point. Absolute zero (-273.15°C) is the lowest possible temperature where molecular motion stops completely. This becomes 0 K on the Kelvin scale, so we add 273.15 to convert from Celsius.

Can Kelvin be negative?

No, Kelvin cannot be negative in classical thermodynamics. The scale starts at absolute zero (0 K), which is the lowest theoretically possible temperature. However, certain quantum systems can exhibit “negative absolute temperature” in specialised contexts, though this refers to a different concept in statistical mechanics.

Why doesn’t Kelvin use the degree symbol?

Unlike Celsius (°C) or Fahrenheit (°F), Kelvin is written without the degree symbol (K) because it’s an absolute scale, not a relative one. It’s named after Lord Kelvin and represents the SI base unit for temperature, similar to how metres or kilograms don’t use symbols.

Is 0 K actually achievable?

According to the third law of thermodynamics, absolute zero (0 K) cannot be reached in practice. Scientists have cooled materials to within billionths of a kelvin above absolute zero, but reaching exactly 0 K would require infinite time and energy. It serves as a theoretical limit rather than an attainable state.

Which countries use Kelvin for everyday temperatures?

No country uses Kelvin for everyday weather reports or daily temperature readings. Kelvin is reserved for scientific, academic, and technical applications. Most countries use Celsius for daily life, whilst the United States primarily uses Fahrenheit.

How do I convert Kelvin back to Celsius?

Simply subtract 273.15 from the Kelvin value. The formula is: °C = K – 273.15. For example, 300 K equals 26.85°C (300 – 273.15 = 26.85).

At what temperature are Celsius and Kelvin the same?

Celsius and Kelvin are never the same numerically because they have different zero points. However, they have the same magnitude—a change of 1°C equals a change of 1 K. The scales run parallel to each other, separated by 273.15 units.

Do I need to round to 273.15 or can I use 273?

For precise scientific work, use 273.15. The additional 0.15 matters in accurate measurements and research. For rough estimates or mental maths, rounding to 273 is acceptable, but you’ll introduce a small error of 0.15 K into your results.