To determine free field thrust of a gas turbine engine, the gas turbine engine may be attached to a movable support, and operated at a selected engine operating point. The thrust applied by the engine to the thrust cradle is measured. The gas turbine engine intake momentum drag generated by airflow into the gas turbine engine intake, the thrust cradle drag force generated by airflow past the moveable support of the thrust cradle, the base drag generated as a result of accelerating nozzle ejector airflow, a pre-streamtube force related to turning of stream lines in the intake air path, a pre-stream tube force related to a bell mouth pull-off force are calculated. Forces due to forward anemometer plane and nozzle static pressures, and a nozzle exit buoyancy force are summed according to respective positive and negative values to determine the free field thrust at the selected engine operating point.