We describe a method for calibration of nanocalorimeters from 573 K to 873 K, using resistive heating and optical pyrometry for temperature measurement. A platinum strip suspended on a silicon nitride membrane serves as both heater and temperature sensor. The calibration described here, relating resistance to temperature, enables subsequent temperature measurement. Measurements of the emissivity of as-deposited and annealed platinum thin films were also performed as a function of wavelength and temperature; these measurements are needed to correct the temperature recorded using the pyrometer. The calibration was validated by measurement of the melting point of a pure aluminum film; the melting point established with a Gaussian fit to the dT/dt data agreed within 0.1% (0.7 K) at 933.5 K. The melting point established from the minimum in the dT/dt plot agreed within 0.6% (5.5 K) at 933.5 K. Finite element modeling was used to characterize the temperature distribution.Highlights► Developed an optical calibration procedure for nanocalorimeters. ► Validated the optical calibration approach by measuring the melting temperature of an aluminum thin film. ► Measured emissivity of platinum thin films as a function of wavelength and temperature. ► Developed a 3D finite element model of a nanocalorimeter to characterize temperature distributions.