It serves as the defining unit of the Planck temperature scale. In this scale the magnitude of the Planck temperature is equal to 1, while that of absolute zero is 0. Unlike Planck length and Planck time, which are defined as the smallest possible measurable units of length and time, Planck temperature is defined as the largest possible measurable unit of temperature. Other temperatures can be converted to Planck temperature units. For example, 0 °C = 273.15 K = 1.9279 × 10−30TP.
As for most of Planck units, a Planck temperature of 1 (unity) is a fundamental limit of quantum theory, in combination with gravitation, as presently understood. In other words, the wavelength of an object can be calculated by its temperature. If an object were to reach the temperature of 1.41 x 1032 Kelvin (TP), the radiation it would emit would have a wavelength of 1.616 x 10−26 nanometers (Planck length), at which point quantum gravitational effects become relevant. At temperatures greater than or equal to TP, current physical theory breaks down because we lack a theory of quantum gravity.