Before you start designing your item, specify a template file which is selected in the dropdown menu Windows ->Preferences ->Template
The choice of this template determines the units of measurement to be used when designing the object. These can be milimeters, inches, meters, feet, etc. In addition, when choosing the template, you will have to approximately define the size of the object to be designed: block of houses, building, piece of furniture, etc. All this affects the accuracy of visualization of objects. If you are working with milimeters, the most appropriate template is “Product Design and Woodworking”, Units: Milimeters.