A vacuum‐type gas‐flow calibrator was designed and constructed for making accurate calibrations of flowmeters needed for the investigation of high‐pressure flames. This calibrator operates by automatically measuring the time required to pressurize a known volume from a near vacuum to 1 atmosphere pressure. The gas volume flow rate is obtained by dividing the calibration volume by the pressurization time and applying corrections from PVT data. This apparatus has been successfully used to calibrate flowmeters for use with hydrogen, oxygen, nitrogen, air, methane, nitric oxide, carbon monoxide, and various homogeneous nonexplosive gas mixtures.