This calculator can determine Field of View and Depth of Field for a particular lens/camera combination. It can also calculate a lens and shooting distance to match that FoV and DoF on a different camera. Adjust "Compare by sensor..." to determine whether all that is compared by Sensor Width, Sensor Height, or Sensor Hypotenuse (Diagonal). Sensor Area and Pixel Density metrics are also presented.
Selecting a pre-defined Camera "locks" Sensor Width / Sensor Height until you set the pre-define Camera list back to "--". Certain pre-defined Cameras also provide (and "lock") Horizontal Pixels and Vertical Pixels.
When specifying a Camera manually, horizontal/vertical dimensions on the same row must be entered together. For example, you cannot specify Taking Camera Sensor Width without specifying Taking Camera Sensor Height.
Otherwise, there are no restrictions - all inputs are optional. Try different combinations to see what information can appear! (for example: Focal Length, Focus Distance, and sensor dimensions will display Dimensional Field of View while if Focus Distance is omitted you'll get Angular Field of View!)
(Note: In most fields, output units will vary with the unit you select for Focus Distance)