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 may include the use of an RBC flocculant, for example polyDADMAC, and an approximate blood hematocrit from the type of animal blood being evaluated, 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 blood hematocrit, and a calculated RBC packing ratio “ii” value for the collection device. A collection device with a BIP is disclosed. 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.