A wound therapy system, comprising: a dressing (112, 2102) sealable over a wound and defining a wound space between the dressing and the wound; tubing (110, 2106) coupled to the dressing (112, 2102) and fluidly communicable with the wound space; a canister (106, 2104) fluidly communicable with the tubing (110, 2106), wherein the canister (106, 2104), the tubing (110, 2106), and the dressing (112, 2102) define a sealed space comprising the wound space; and a therapy unit (102, 2108) coupled to the canister (106, 2104) and comprising: a pneumatic pump (120, 2122) fluidly communicable with the sealed space; a sensor (130, 2124) configured to measure a pressure in the sealed space; a valve (113b, 2126) positioned between the sealed space and a surrounding environment and controllable between an open position and a closed position; and a control circuit configured to determine a volume of the wound space by performing the steps of: control the pneumatic pump (120, 2122) to remove air from the sealed space to establish a negative pressure in the sealed space; control the valve (113b, 2126) to repeatedly alternate between the open position and the closed position to allow a controlled rate of airflow through the valve (113b, 2126); receive measurements of the pressure in the sealed space from the sensor (130, 2124); and determine a volume of the wound space based on the measurements of the pressure. a dressing (112, 2102) sealable over a wound and defining a wound space between the dressing and the wound; tubing (110, 2106) coupled to the dressing (112, 2102) and fluidly communicable with the wound space; a canister (106, 2104) fluidly communicable with the tubing (110, 2106), wherein the canister (106, 2104), the tubing (110, 2106), and the dressing (112, 2102) define a sealed space comprising the wound space; and a therapy unit (102, 2108) coupled to the canister (106, 2104) and comprising: a pneumatic pump (120, 2122) fluidly communicable with the sealed space; a sensor (130, 2124) configured to measure a pressure in the sealed space; a valve (113b, 2126) positioned between the sealed space and a surrounding environment and controllable between an open position and a closed position; and a control circuit configured to determine a volume of the wound space by performing the steps of: control the pneumatic pump (120, 2122) to remove air from the sealed space to establish a negative pressure in the sealed space; control the valve (113b, 2126) to repeatedly alternate between the open position and the closed position to allow a controlled rate of airflow through the valve (113b, 2126); receive measurements of the pressure in the sealed space from the sensor (130, 2124); and determine a volume of the wound space based on the measurements of the pressure. a pneumatic pump (120, 2122) fluidly communicable with the sealed space; a sensor (130, 2124) configured to measure a pressure in the sealed space; a valve (113b, 2126) positioned between the sealed space and a surrounding environment and controllable between an open position and a closed position; and control the pneumatic pump (120, 2122) to remove air from the sealed space to establish a negative pressure in the sealed space; control the valve (113b, 2126) to repeatedly alternate between the open position and the closed position to allow a controlled rate of airflow through the valve (113b, 2126); receive measurements of the pressure in the sealed space from the sensor (130, 2124); and determine a volume of the wound space based on the measurements of the pressure.