# joule per kelvin

##### SI coherent derived unit whose name and symbol includes an SI coherent derived unit with a special name and symbol
Name Symbol Quantity Expressed in terms of SI base units
joule per kelvin J/K heat capacity,
entropy
kg m2 s−2 K−1

### Definition

The joule per kelvin, symbol J/K, is the SI coherent derived unit of heat capacity, and entropy.

The fixed numerical value of the Boltzmann constant, k, is defined to be exactly 1.380 649 × 10‑23 when expressed in the unit joule per kelvin, symbol J K-1.

$k \mspace{6mu} = 1.380 \mspace{4mu} 649 \times 10^{-23} \mspace{6mu} \text{J} \mspace{6mu} \text{K}{^{-1}}$

Inverting this relation gives an exact expression for the joule per kelvin in terms of the SI defining constant k :

$1 \mspace{6mu} \text{J} \mspace{6mu} \text{K}{^{-1}} \mspace{6mu} = \dfrac{k}{1.380 \mspace{4mu} 649 \times 10^{-23}}$

The effect of this definition is that one joule per kelvin is exactly 11.380 649 × 10−23 of the Boltzmann constant.