Celsius to Kelvin Calculator – Convert °C to K and Vice Versa

Temperature Converter

Temperature in Celsius (°C)

The Celsius to Kelvin Calculator converts temperatures between Celsius (°C) and Kelvin (K), the SI base unit of temperature. Kelvin is an absolute scale starting at absolute zero (-273.15°C), making it essential for scientific calculations like the ideal gas law, thermodynamics, and astronomy. This calculator provides step‑by‑step explanations, making it ideal for students, scientists, and anyone working with temperature conversions in science and engineering.

Celsius to Kelvin Formula

Formula: K = °C + 273.15

Example: 0°C → 0 + 273.15 = 273.15 K

Example: 100°C → 100 + 273.15 = 373.15 K

How to Convert Celsius to Kelvin (Step‑by‑Step)

Start with the temperature in Celsius (°C).
Add 273.15 to the value.
The result is the temperature in Kelvin (K).

Example: 25°C → 25 + 273.15 = 298.15 K

Reverse Conversion – Kelvin to Celsius

Formula: °C = K - 273.15

Example: 273.15 K → 273.15 - 273.15 = 0°C

Example: 373.15 K → 373.15 - 273.15 = 100°C

Common Temperature Reference Points

Description	°C	K
Absolute zero	-273.15	0
Water freezes	0	273.15
Room temperature	20-22	293.15-295.15
Body temperature	37	310.15
Water boils	100	373.15

Real‑World Applications of Kelvin

Physics & chemistry: Ideal gas law (PV = nRT) requires Kelvin to avoid negative temperatures.
Astronomy: Stellar temperatures (e.g., Sun's surface ~5778 K).
Engineering: Thermodynamics, heat engines, and cryogenics.
Meteorology: Some scientific weather models use Kelvin.

What is Absolute Zero?

Absolute zero (0 K) is the lowest possible temperature where all molecular motion stops. It is equivalent to -273.15°C. Kelvin was developed by Lord Kelvin (William Thomson) in 1848 as an absolute scale. Unlike Celsius, Kelvin does not use the degree symbol – it is simply "K".

Absolute Kelvin & Celsius Temperature Reference Table

Physical Benchmark Point	Celsius (°C)	Kelvin (K)	Fahrenheit (°F)	Thermodynamic & Physics Note
Absolute Zero	-273.15°C	0.00 K	-459.67°F	Complete cessation of classical molecular motion
Liquid Helium Boiling Point	-268.93°C	4.22 K	-452.07°F	Superfluidity helium transition state
Liquid Nitrogen Boiling Point	-195.79°C	77.36 K	-320.42°F	Industrial cryogenics & sample freezing
Dry Ice Sublimation Point (CO2)	-78.50°C	194.65 K	-109.30°F	Solid carbon dioxide sublimation
Water Freezing Point	0.00°C	273.15 K	32.00°F	Standard ice-water equilibrium at 1 atm
Room Temperature (Standard)	25.00°C	298.15 K	77.00°F	Standard IUPAC ambient lab temperature
Human Body Temp (Normal)	37.00°C	310.15 K	98.60°F	Physiological human norm
Water Boiling Point	100.00°C	373.15 K	212.00°F	Liquid-vapour equilibrium at 1 atm
Sun's Photosphere Surface	5,504.85°C	5,778.00 K	9,940.73°F	Solar blackbody radiation spectrum

Common Mistakes When Converting Celsius to Kelvin

Forgetting to add 273.15: Some mistakenly add 273 instead, which introduces a small error for precise work.
Using the degree symbol: Kelvin is written as "K", not "°K" (the degree symbol is not used).
Subtracting instead of adding: The correct direction is °C + 273.15 = K.

Why Kelvin is the Scientific Standard

Kelvin is an absolute scale, meaning 0 K represents the complete absence of thermal energy. Many physical laws (e.g., Charles's law, Gay‑Lussac's law) become simpler and more intuitive when using Kelvin because they involve direct proportionality with temperature. For example, doubling the Kelvin temperature doubles the pressure (at constant volume), but doubling Celsius does not.

Use this celsius to kelvin calculator for science homework, lab work, or any situation requiring accurate temperature conversion. The step‑by‑step output ensures you understand the simple addition/subtraction involved.

Step‑by‑Step Manual Example

Convert 25°C to Kelvin: 25 + 273.15 = 298.15 K

Convert 400 K to Celsius: 400 - 273.15 = 126.85°C

Frequently Asked Questions about Celsius to Kelvin

What is Kelvin (K)?

Kelvin is the SI base unit of thermodynamic temperature. It is an absolute scale where 0 K represents absolute zero – the theoretical state where thermal energy and atomic motion cease.

What is the formula for converting Celsius (°C) to Kelvin (K)?

The exact formula is: K = °C + 273.15. For example, 0°C = 273.15 K, 25°C = 298.15 K, and 100°C = 373.15 K.

What is the formula for converting Kelvin (K) to Celsius (°C)?

The exact formula is: °C = K - 273.15. For example, 273.15 K = 0°C, 373.15 K = 100°C, and 0 K = -273.15°C.

Why is the degree symbol (°) omitted for Kelvin?

Unlike Celsius and Fahrenheit, Kelvin is an absolute unit of measurement rather than an arbitrary degree scale. Therefore, it is written as 'K' (e.g. 300 K), never '°K'.

Why do scientists use Kelvin instead of Celsius for thermodynamic laws?

Kelvin eliminates negative temperature values in physical equations like the Ideal Gas Law ($PV = nRT$) and Charles's Law, ensuring gas volume and pressure remain strictly non-negative.

What is room temperature in Kelvin?

Standard room temperature (20°C to 25°C) equals approximately 293.15 K to 298.15 K.

What is the boiling point of liquid nitrogen in Celsius and Kelvin?

Liquid nitrogen boils at -195.79°C, which equals 77.36 K.

Can Kelvin temperatures be negative?

In classical thermodynamics, Kelvin cannot be negative because 0 K is the absolute lower limit of atomic kinetic energy. (Quantum spin systems can exhibit negative effective temperatures, but not in classical state space).