Sep 17, 2011

Understanding Units in AutoCAD

In AutoCAD setting up a unit is very much important in every drawing. Sometimes you are working with drawings which are not yours. When you don't know what is the unit used you have the problems in printing or plotting since printers and plotters knows millimeters and inches only. For example, our buyer gives as a drawing, a dining table which measure 112 x 52 x 30 height. When I enter units command what I see there is in millimeters. And so when I'm going to plot this in 1:1 scale that would be very small if I'm going to use a millimeters unit in plotter. And so I conclude, this should be in inches because, the standard height of a dining table is 30”.

Technically speaking AutoCAD software does not care anything about your units, whether it is inches, millimeters or in meters. That is the reason why AutoCAD has a lot of choices with units. There is even light year unit which is used to measure the light travel in space, distance of stars, and so we can even create the entire universe in AutoCAD in 1:1 scale.



Every object you draw is measured in units. You determine the value of the units within AutoCAD before you draw. For example, in one drawing, a unit might equal one millimeter of the real-world object. In another drawing, a unit might equal an inch.

To format drawing units

1) From the Format menu, choose Units, or on command line, type units->enter.
2) In the Drawing Units dialog box, set the unit values for your drawing. As you change unit settings, AutoCAD shows examples under Sample Output.

Under Length, select a unit type and level of precision.
Under Drawing units for AutoCAD DesignCenter blocks, select the unit that you want AutoCAD to use to scale blocks, images or other content inserted into the drawing. If you do not want AutoCAD to scale inserted content, select Unitless.
Under Angle, select an angle type and precision.
To specify an angle direction, choose Direction, and then select the base angle in the Direction Control dialog box.

The angle direction controls the point from which AutoCAD measures angles and the direction in which they are measured. The default is 0 degrees on the right side of the figure, measured counterclockwise. If you select Other, you can enter an angle, or choose Angle to specify an angle using your pointing device.

3) Choose OK to exit each dialog box.

Formatting units in architectural

In architectural almost all units used is in meters. For example, when we draw a floor plan measuring as 3.70 x 3.2 meters bedroom, we cannot enter exactly or used exactly as 3.7 x 3.2 meters. Why? If we're going to use it that would be very small in plotted drawing, since plotters do not use meters but in millimeters and inches only. Since AutoCAD use units as a unit this can be either in millimeters or in meters.

How to solve the problem?

The only solution is set up your drawing to millimeters to draw your floor plan in millimeters, so your floor plan dimension is now 3700 x 3200 millimeters. Why is that? Conversion factor; 1 meter = 1000 millimeters.

See sample drawing.


When you make dimensions in your drawing it should look like the image above. However, this is not good to see for the construction when only a carpenter will read it. The carpenter will think this as meters so this would be very big if the scale shown is 1:100 meters. Imagine 3200 meters, that is 3.2 kilometers. What will happen next will be a disaster.

Display Dimensions in Meters

What we're going to present here is to display the dimensions in meters so that it will coincide into the 1:100 meters scale, even if the drawing was drawn in millimeters, which looks like this:


We need only to scale the dimensions so that it measures exactly as in meters, even if our drawing is in millimeters.


During our previous years in drafting when CADD is not common to all, we used a triangular scale to draw a scaled drawings. Some of us just used the instrument without realizing how it works.

Scaling is important to proportion the drawings and to see what it looks like.

In scale 1:100 meters this means that we reduce the drawing in to 100x smaller. And so this is equal to 1 meter divided by 100 or 1/100 meter. If we find the fraction of this using a calculator, we get 0.01 meter and that is equal to 1 cm.

And so, when we see a blue print of a house, building etc. that has 1:100 meters scale, it uses 1 cm as 1 meter. If you have and ordinary ruler, you can measure the blue print. You will see for example 5cm is equal to 5 meters in 1:100 meters scale.

To scale a dimensions in AutoCAD.

1.)Select a dimension line.
2.)On command line type PROPERTIES->ENTER. (a dialog box comes out) see below


3.)As you can see you need to edit the Dim Scale Linear.
4.)Type-> 0.0010-> enter (automatically you've selected dimension has changed)
Note: 0.0010 = 1/1000 mm (this is our scale factor since we use mm in our drawing)
5.)Finish editing all the dimensions by using MATCHPROP command.


So now your drawing is actual in millimeters but your dimensions are in meters.
That's all.

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