A blood volume monitor (10) includes a carrier (12) mountable about a part of a body of a subject. A measuring arrangement (13) is mounted on the carrier (12). The measuring arrangement (13) comprises at least one element (14, 18) configured to provide volume data relating to a volume of the part of the body of the subject underlying the carrier (12) and for measuring change in volume of the part of the body of the subject underlying the carrier (12) and for outputting response signals representative of the change in volume. A control unit (20) is in communication with the measuring arrangement (13) to process data output by the measuring arrangement (13) to determine, using the volume data, the volume of the part of the body of the subject underlying the carrier (12) and to determine blood volume in the part of the body of the subject, the control unit (20) using the response signals received from the measuring arrangement and the determined volume of the part of the body to determine the blood volume.
