1.5.2 - Setting Units and Scale

Now that the basic file is set up, you will start your design drawing its layout as shown in Fig.1.5.0.1. (In this step you will not set dimensions and text, and the color will be black).

Before you start to draw, you decide on the units of measurement to be used in the drawing, and set the format, precision, and other conventions to be used in coordinates and distances.

Every object you create is measured in drawing units. Before you start to draw, you must decide what one drawing unit will represent based on what you plan to draw. Then you create your drawing at actual size with that convention.

AutoCAD does not care; it gives you a system and lets you adapt it to any situation or design. Then, you just draw in real-life units or, as we say in CAD, 1-to-1 units. This is the Golden Rule of AutoCAD. Always draw everything to real-life size. Do not scale objects up or down.

For example, the objects in  a drawing might represent a house with external dimensions that are each 12,5 and 10,00 meters long, or a section of a mechanical part that is measured in millimeters. In the first case the units will represent meters, this means that when you type 2 you mean 2 meters, in the second case when you type 200, you mean millimeters.

The default unit system in AutoCAD, until you change it, is a simple decimal system of the type we use in everyday life. However, it is unitless, meaning that the 2 or 3 you entered could have been anything—feet, inches, yards, meters, miles, or millimeters.

Architects drawing in imperial unit system, prefer their distances broken down to feet and inches, because it is always easier to understand and visualize a distance of 22'-6" than 270". To switch to architectural units, type in units and press Enter, or select Format → Units… from the cascading menus, and the dialog box in Figure 1.5.2.1 appears.

Simply select Architectural from the drop-down menu at the upper left and ignore the rest of the options in the dialog box; there is no need to change anything else at this point. Now, as you draw and enter in units, they are recognized as feet or inches. To enter in 5 feet (such as when using the offset command), type 5'. To enter in 5 inches, there is no need for an inch sign, just type in the number 5; AutoCAD understands. To mix feet and inches, type in 5'6, which is of course 5'-6"; there is no need for a hyphen either.

For our project we will use the decimal system. On the Drawing Units table select the following:

Length ► Type = Decimal, Precision = 0.000, Insertion Scale = Meters, and Angle ► Type = Decimal Degrees, Precision = 0.00.

It means that if you want to draw a line with length 2 meters, you will type 2, if the length of the line is 2 meters and 30 centimeters you will type 2.30.