A wound therapy system comprising: a therapy device comprising: a canister configured to collect wound exudate from a wound; and a pump fluidly coupled to the canister and configured to draw a negative pressure within the canister; tubing having a first end and a second end (1 10b), the first end being attached to and fluidly coupled to the canister; a valve coupled to the tubing at a position located between the first end (1 10a) and the second end (1 10b) of the tubing, the valve configured to prevent flow if a threshold minimum negative pressure is not met and to permit flow if the threshold negative pressure is met; a first tubing portion defined between the first end (1 10a) of the tubing and the valve and a second tubing portion defined between the second end of the tubing and the valve; an opening formed through the first tubing portion, the opening configured to allow for fluid communication between the first tubing portion and an ambient pressure atmosphere, wherein the second end (1 10b) of the tubing is attached to a wound dressing configured to be sealed to a surface to define a treatment space, the canister being in fluid communication with the treatment space when the valve is subject to a pressure that is less than or equal to the threshold minimum negative pressure; characterized by a controller configured to: operate the pump to draw a predetermined first negative pressure in the canister, the first predetermined negative pressure being greater than the threshold minimum negative pressure; and calculate a first volume based on a measured time required for pressure within the canister to increase from the predetermined first negative pressure to a predetermined baseline pressure. a therapy device comprising: a canister configured to collect wound exudate from a wound; and a pump fluidly coupled to the canister and configured to draw a negative pressure within the canister; a canister configured to collect wound exudate from a wound; and a pump fluidly coupled to the canister and configured to draw a negative pressure within the canister; tubing having a first end and a second end (1 10b), the first end being attached to and fluidly coupled to the canister; a valve coupled to the tubing at a position located between the first end (1 10a) and the second end (1 10b) of the tubing, the valve configured to prevent flow if a threshold minimum negative pressure is not met and to permit flow if the threshold negative pressure is met; a first tubing portion defined between the first end (1 10a) of the tubing and the valve and a second tubing portion defined between the second end of the tubing and the valve; an opening formed through the first tubing portion, the opening configured to allow for fluid communication between the first tubing portion and an ambient pressure atmosphere, wherein the second end (1 10b) of the tubing is attached to a wound dressing configured to be sealed to a surface to define a treatment space, the canister being in fluid communication with the treatment space when the valve is subject to a pressure that is less than or equal to the threshold minimum negative pressure; characterized by a controller configured to: operate the pump to draw a predetermined first negative pressure in the canister, the first predetermined negative pressure being greater than the threshold minimum negative pressure; and calculate a first volume based on a measured time required for pressure within the canister to increase from the predetermined first negative pressure to a predetermined baseline pressure. operate the pump to draw a predetermined first negative pressure in the canister, the first predetermined negative pressure being greater than the threshold minimum negative pressure; and calculate a first volume based on a measured time required for pressure within the canister to increase from the predetermined first negative pressure to a predetermined baseline pressure.