Units & Conversion · 摄氏与开尔文（Celsius & Kelvin） · Updated 2026-10-25
What Is Celsius & Kelvin?
Definition
Kelvin shares the Celsius interval (a 1 K change equals a 1 °C change) with its zero at absolute zero (−273.15 °C, the theoretical floor of molecular motion). Science requires kelvin: the ideal gas law PV=nRT, Stefan–Boltzmann radiation and color temperature (daylight 5500K) are all defined on absolute temperature. 0 K is approachable but unreachable (third law). Daily life uses °C; Fahrenheit survives in a handful of countries.
Formula
T(K) = t(°C) + 273.15; t(°F) = t(°C)×9/5 + 32
Worked Example
Standard conditions 25 °C = 298.15 K; an incandescent "2700K" color temperature corresponds to a ~2427 °C blackbody — the K there is an equivalent blackbody temperature, not the filament reading.
Common Misconception
"Keep cooling and you reach 0 K" — the third law forbids it. And offsets may shift by 273.15, but any formula using temperature ratios (Carnot efficiency = 1−Tc/Th) demands absolute temperature; plugging in °C yields absurd negative efficiencies.
Matching Calculators
Related Terms
Keep Exploring
Browse the full glossary, or head back to the homepage for 1,435 free online calculators.
Back to glossary