Kelvin to Celsius Converter
Convert Kelvin to Celsius and Fahrenheit for science, physics and chemistry.
How to use this kelvin to celsius
- 1Enter a temperature in Kelvin.
- 2The converter shows Celsius and Fahrenheit instantly.
- 3For scientific and physics contexts, Kelvin is the standard — use Celsius output for practical communication.
- 4Key Kelvin reference points: 0 K = absolute zero, 273.15 K = 0°C (water freezes), 373.15 K = 100°C (water boils), 293 K = 20°C (room temperature).
- 5For color temperature (LEDs, photography lighting), Kelvin values range from 2,700 K (warm white) to 6,500 K (daylight).
- 6For stellar physics, stars are classified by surface temperature in Kelvin — the Sun is ~5,778 K.
How it's calculated
°C = K − 273.15. °F = °C × 9/5 + 32.
About the Kelvin to Celsius
The Kelvin scale is the International System of Units (SI) standard for temperature, and unlike Celsius and Fahrenheit, it starts at absolute zero — the theoretical minimum temperature at which thermal motion would cease. This property makes Kelvin indispensable in physics, chemistry, and astronomy, where temperature appears in equations that require a scale with a meaningful zero point.
The Kelvin scale is directly related to Celsius by a simple offset: K = °C + 273.15. One Kelvin equals exactly one degree Celsius in scale size — only the zero reference differs. Water freezes at 273.15 K (0°C) and boils at 373.15 K (100°C) at standard atmospheric pressure. The −273.15 offset reflects the location of absolute zero on the Celsius scale, established from thermodynamic principles by Lord Kelvin (William Thomson) in the 19th century.
The ideal gas law (PV = nRT) and many other fundamental equations in thermodynamics and physical chemistry require temperature in Kelvin to produce correct results. In these equations, T is absolute temperature — a temperature that doubles in Kelvin genuinely means twice the thermal energy. If Celsius were used, doubling from 20°C to 40°C would suggest doubled energy, but the actual thermal energy ratio would be 313.15/293.15 = 1.068, not 2. Kelvin makes these energy relationships mathematically direct.
Astronomy uses Kelvin universally because the temperatures involved range from near absolute zero (cosmic microwave background: 2.7 K) to millions and billions of degrees in stellar interiors and quasars. The surface temperature of stars determines their color in the Hertzsprung-Russell diagram: M-class (red) stars are 2,400–3,700 K, G-class stars like our Sun are 5,300–6,000 K, A-class (white-blue) stars are 7,500–10,000 K, and O-class (blue) stars exceed 30,000 K. This directly connects the abstract Kelvin scale to the visible colors of stars in the night sky.
Color temperature in lighting and photography borrows the Kelvin concept to describe the color quality of light sources by analogy to black-body radiation: a source described as "6,500 K" doesn't need to be that temperature, but its light has the same spectral color as a black body at 6,500 K. This convention makes Kelvin useful to photographers, videographers, cinematographers, and interior designers who need to match light sources or describe the warmth/coolness of illumination precisely.
Frequently asked questions
What is 0 Kelvin in Celsius?
0 K = −273.15°C — absolute zero, the theoretical lowest possible temperature where all molecular motion ceases. No physical object has ever reached absolute zero, though laboratory experiments have come within billionths of a degree.
What is room temperature in Kelvin?
Standard room temperature is approximately 293–298 K, equivalent to 20–25°C (68–77°F). The scientific standard temperature (used in chemistry and physics calculations) is 298 K = 25°C exactly.
Why does science use Kelvin instead of Celsius?
The Kelvin scale starts at absolute zero and has no negative values, making it mathematically convenient for thermodynamic calculations. Many physical laws (ideal gas law, Wien's displacement law, black-body radiation) require temperature in Kelvin to produce correct results. Using Celsius or Fahrenheit in these equations would give wrong answers because those scales have arbitrary zero points unrelated to thermal energy.
What is color temperature in Kelvin for photography and lighting?
Color temperature describes the warmth or coolness of light: 2,700–3,000 K = warm white (incandescent/candle-like), 3,500–4,100 K = neutral white (office/retail), 5,000–5,500 K = cool daylight, 6,500 K = blue-tinted daylight. Camera white balance settings use Kelvin for precise color correction. LED bulb packaging now commonly displays Kelvin instead of just 'warm' or 'cool'.
What is the surface temperature of the Sun in Kelvin?
The Sun's surface (photosphere) temperature is approximately 5,778 K (5,505°C / 9,941°F). The Sun's core is approximately 15 million K. By comparison, the surface of a red star can be as cool as 3,500 K, while blue-white stars exceed 10,000 K. Color temperature in lighting (2,700–6,500 K) deliberately mimics the range of light color emitted by objects at those temperatures.