The first checkbox in the Plate Meshing Wizard is Select Model Units.
Click on the Unit System drop down menu and select the suitable type of units. Selecting Mixed type will allow choosing all the units. After selecting the units, click OK to save the selection.
If you are using the Plate Meshing Wizard to create the mesh, it is recommended that you use millimeters, centimeters, or inches. Using meters is not advised as the meshing tolerance in meters has to be very small.