A wound therapy system includes a dressing sealable over a wound and defining a wound space between the dressing and the wound, tubing fluidly communicable with the wound space, and a canister fluidly communicable with the tubing. The canister, the tubing, and the dressing define a sealed space that includes the wound space. The wound therapy system also includes a therapy unit coupled to the canister. The therapy unit includes a sensor configured to measure a pressure in the sealed space, a valve positioned between the sealed space and a surrounding environment and controllable between an open position and a closed position, and a control circuit. The control circuit is configured to control the valve to alternate between the open position and the closed position to allow airflow through the valve, receive measurements from the sensor, and determine a volume of the wound space based on the measurements.