Disclosed are methods, materials and devices for approximation of blood volume in a fluid, such as in a biological fluid collected during a surgical procedure. The method and devices include the use of a RBC flocculant, such as polyDADMAC, and an approximate blood hematocrit for the type of animal, as well as a calculated RBC packing ratio corresponding to the collection device being used. Also provided is a Blood Indicator Panel (BIP), comprising a series of markings calculated from an observed red blood settlement volume, the average animal type hematocrit, and a calculated RBC packing ratio “η” value for the collection device. Pediatric (about 200 ml or 250 ml size container), adult human (about 1,000 ml-1,500 ml) and veterinary (about 500 ml-2,500 ml) collection containers are also disclosed, that include a RBC flocculant, for use in approximating blood volume in a fluid.