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Ice point (0 °C in kelvin)

T0=273.15 KT_0 = 273.15\ \text{K}
Value273.15 K
Use in the calculator →
StatusExact by definition: no uncertainty
SourceSI Brochure, 9th edition (2019)
CategoriesThermodynamicEngineering & Trade
Ice point (0 °C in kelvin) in every temperature unit
UnitValue
degree Celsius0 °C
degree Fahrenheit32 °F
kelvin273.15 K
degree Rankine491.67 °R
kilokelvin0.27315 kK
6 more temperature units
nanokelvin273,150,000,000 nK
microkelvin273,150,000 μK
millikelvin273,150 mK
degree Réaumur0 °Ré
megakelvin0.00027315 MK
gigakelvin2.7315000e-07 GK

Learning zone

This is the offset in the definition of the Celsius scale, t/°C = T/K − 273.15, and it is exact by definition rather than measured. It is also the single most common source of arithmetic error in thermodynamics: gas laws, Carnot efficiency and radiation calculations all demand absolute temperature, and feeding them Celsius produces answers that look plausible and are badly wrong.

The number is not quite the freezing point of water. Air-saturated water at 1 atm freezes at 273.1500 K to within a fraction of a millikelvin by happy historical accident, but the ice point stopped being the definition in 1954, when the scale was anchored to the triple point instead. Note also the difference between a temperature and a temperature difference: a change of 1 °C equals a change of 1 K exactly, with no offset at all.

Used by 4 solvers

Carnot Efficiency

η=1−TcTh\eta = 1 - \frac{T_c}{T_h}

Charles's Law

V1T1=V2T2\frac{V_1}{T_1} = \frac{V_2}{T_2}

Combined Gas Law

P1V1T1=P2V2T2\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}

Ideal Gas Law

PV=nRTP V = n R T
Revised 29 August 2026
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formula.expert. (2026, August 29). Ice point (0 °C in kelvin). https://formula.expert/constants/ice-point-temperature