Compact devices are provided to measure hematocrit of a blood sample. These devices include first and second chambers that receive respective portions of a blood sample via respective filters. The material of the filters prevents passage of red blood cells while permitting passage of blood plasma. One of the filters has one or more holes to permit the passage of whole blood. Thus, when an example device is presented with a sample of blood, one of the chambers contains whole blood and the other contains blood from which the red blood cells have been filtered. Electrodes in each of the chambers can then be used to detect the impedances of the whole blood and the filtered blood, and the detected impedances can be used to determine a hematocrit of the sample of blood.