= Wien displacement constant
{c}
{title2=$b$}
{wiki}
The <Wien displacement constant> is the <constant of proportionality> $b$ in $\lambda_{\max}T=b$. From the exact <International System of Units> values of the <Planck constant>, <speed of light> and <Boltzmann constant>,
$$
b=\frac{(6.62607015\times10^{-34})(299792458)}{(1.380649\times10^{-23})(4.9651142317\ldots)}\,\mathrm{m\,K}
\simeq2.897771955\times10^{-3}\,\mathrm{m\,K}.
$$
The units follow from $hc/k_B$: $(\mathrm{J\,s})(\mathrm{m\,s^{-1}})/(\mathrm{J\,K^{-1}})=\mathrm{m\,K}$. The defining constants are exact; the displayed decimal is rounded. <Fundamental Physical Constants — Complete Listing by National Institute of Standards and Technology and others>[Wien wavelength displacement law constant and Wien frequency displacement law constant]{ref}
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