The paper describes the unified mathematical procedures of transient methods for measuring surface heat transfer rates. Three heat flux gauges are discussed : thin film, thick-wall gauges placed on semi-infinite substrates and thin-skin calorimeters. The aim of this paper is to present a method for a simple and accurate determination of the time-varying heat transfer coefficient Cor heat flux) given an accurate temperature history of the body at a selected point beneath the surface. The interior temperature measurements are converted into local instantaneous heal transfer coefficients by solving the inverse heat conduction problem for the gauge. The effect of the inaccuracies in the measurement of the interior temperature was eliminated by cubic spline smoothing or digital filtering of the raw interior temperature data prior to using it in the inverse heat conduction analyses. General case closed form equations for instantaneous surface heat flux, or heat transfer coefficient, are developed.