A method and device performing the method for estimation of cell count, such as sperm cell count, is disclosed. The device may be a kit including a cartridge configured to hold fluid, such as seminal fluid, and an instrument configured to centrifuge the cartridge. The cartridge and instrument are configured such that, during operation or centrifugation, they are securely attached to each other. The cartridge has a component with a defined cross-sectional volume. The defined cross-sectional volume is used to mark the component with markings, allowing a user of the device to read the markings and estimate cell volume and, thus, concentration. Various embodiments of the device are disclosed.