NPL is the custodian of the UK national standards, and, in particular, the primary realisation of the ITS-90 and is a recognised world leader in temperature measurement. NPL realises and disseminates ITS-90 from 4 K to 3000 °C and has ultra-low uncertainties in both contact and non-contact thermometry. The NPL thermometry group has extensive and well established leading primary acoustic thermometry facilities. It undertook measurements of the Boltzmann constant with sub-ppm uncertainty and also very low uncertainty thermodynamic evaluation of the ITS-90 by acoustic gas thermometry.