A monitoring system for a dual-stage, pressure-activated, mixed fluid gas shock strut, may comprise a controller, and a tangible, non-transitory memory configured to communicate with the controller, the tangible, non-transitory memory having instructions stored thereon that, in response to execution by the controller, cause the controller to perform operations comprising receiving, by the controller, a primary chamber temperature sensor reading, receiving, by the controller, a primary chamber pressure sensor reading, receiving, by the controller, a shock strut stroke sensor reading, and calculating, by the controller, an oil volume in a primary chamber of the shock strut. The instructions may cause the controller to perform further operations comprising calculating, by the controller, a number of moles of gas in a primary chamber of the shock strut and calculating, by the controller, a number of moles of gas in a secondary chamber of the shock strut.