Abstract: A wound therapy system includes a dressing sealable over a wound, a conduit comprising a first inner diameter, coupled to the dressing, and fluidly communicable with the wound space, and a canister fluidly communicable with the conduit. A therapy unit is coupled to the canister and includes a pump, a sensor configured to measure a pressure, a valve controllable between an open position and a closed position, and a control circuit. The control circuit is configured to control the pneumatic pump to remove air to establish a negative pressure, control the valve to repeatedly alternate between the open closed positions to allow a controlled rate of airflow through the valve, receive measurements of the pressure from the sensor, and determine a volume of the wound space based on the pressure measurements. A portion of the conduit comprises a second inner diameter that is less than the first inner diameter.