HOW TO USE UNITS AND SCALES IN AUTOCAD?

This is one of the basic and fundamental concepts a newcomer to Autocad should learn. One cannot start creating a sensible drawing until they are familiar with units, scale and the commands to control them. In this tutorial we’ll discuss the concepts of Units and Scales.

Before we get into commands there are two Frequently Asked Questions (FAQ’s) on Units and Scales. Lets us first try to answer them.

1.      Why should I set Scale in Autocad?  

No matter what you draw in Autocad it will be drawn in full size, i.e. it will be in the scale ratio of 1:1. You don’t have to worry of about setting drawing scales as you do when using on drawing board. While drawing on a sheet of paper be it A0, A1, A2 or A3 you should decide the drawing scale, whether you going to draw in the ratio of 1:20 or 1:200 based on the size of the paper and the size of the drawing. In Autocad you do not need to decide upon a drawing scale until you come to print the drawing. The scaling of the drawing takes place at the printing stage. This will give you the ability to measure lengths, areas and volumes within the Autocad drawing and you no need to compensate on any scale factor. 

2.      What Units should I use?
 

      In most parts of the World it is the common practice to use Meters or millimeters. Which of these two units you will use rely on the type of drawing you create? For example if you are creating an automobile/mechanical component you would probably be working in millimeters or on the other hand if you’re creating a landscape you would probably be working in meters. Most Architects and Engineers prefer to work in Meters. Autocad supports both System of International (SI units) and Imperial system units. Imperial system is largely used by American Autocad users where Feets and Inches are still in common practice. 

The following Table shows you the Different type of units available in Autocad for you to work with. 

UNIT TYPE	DESCRIPTION	DRAWING UNITS
Decimal	Metric or SI Units	1.5000
Scientific	Decimal Value raised to a power	1.5 E+03
Engineering	Feet and Decimal inches	1.5' - 1.5"
Architectural	Feet and Fractional inches	0' - 1 1/2"
Fractional	Whole Numbers and Fractions	1 1/2 - 1500

 

Units:

Units Dialogue Box

AutoCad Command : Units

Alias Command : un

Pull Down : Format > Units…

Let’s take a look at units command -

Units Command can be accessed in different ways. You can navigate using pull down menu using mouse or just use keyboard and enter ‘Units’ in the command window. You can also bring up Units Dialogue box by just entering the alias command ‘un’.

When you start units command a Drawing units Dialogue box will come up as shown above. The dialogue box is divided into five main sections. The Top most sections include “Length”  and  “Angular” Sections. Length Sections include linear units such as Decimal, Engineering, Scientific, Architectural and Fractional units.  Angular Section Includes Angular units like Decimal Degrees, Deg/Min/Sec, Grads, Radians and Surveyor units.

Both Length and Angular Sections are provided with Precisions. By default, Autocad sets linear unit precision to four places of decimal, so the distance appear in the form 0.0000. Angular unit precision is set to whole degrees only. In addition, the Angles Section also allows you to specific the directions in which angles are measured. See the below picture. 

Direction Control

Using the direction control you will have the ability measure and position of the start angle of the angular units. By default the Base angle will be set to zero angle (East) with its angles increasing in an anti-clockwise direction.  The default setting will do well for most of the part. However there may be at times you may have to use zero angle at 9 o clock position (West) and the increasing angles in clockwise direction. For example while drawing geographical maps or surveyors drawings; this situation enables you to specify angles with respect to West.

The Middle Section consists of Insertion Scale. Insertion Scale lets you to control the unit of measurement for blocks and drawings that are inserted into the current drawings. It will automatically scales the drawings or blocks when inserted into the current drawings when the units are different from the units specified. 

The Bottom Section consists of Lighting. It enables you to control the unit of measurement for the intensity of photometric light in the current drawings. This option is occasionally used and not as important as compared to the latter ones.

By this I am wrapping up the session on Units and Scales. Hope you liked. Feel free to live your comments for the above tutorial and I’ll be glad to answer your queries.