A volume of a wound is estimated using a dynamic pressure response measured during instillation of fluid to the wound using a negative pressure wound therapy system. A previously estimated wound volume may be used to detect and prevent overfill of fluid to the wound during future instillation events. For example, real-time pressure measurements may be compared to model data representative of expected pressure at a wound having a volume equal to the previously estimated wound volume, with instillation being stopped if the observed pressure varies from the expected pressure. A comparison of a total volume of fluid instilled to the wound may also be compared to the previously estimated wound volume to prevent overfill. The comparison of wound volume estimated based on an instillation event may also be compared to a wound volume estimated using other methods to provide a higher confidence wound volume estimate.