An inkjet printhead device, fluid ejection device and method thereof are disclosed. The fluid ejection device includes a fluid supply chamber to store fluid, an ejection chamber including a nozzle and a corresponding ejection member to selectively eject the fluid through the nozzle, and a channel to establish fluid communication between the fluid supply chamber and the ejection chamber. The fluid ejection device also includes a pressure sensor unit having a sensor plate to output a voltage value corresponding to a cross-sectional area of an amount of fluid in the at least ejection chamber.