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Concept:
This tutorial will explain the different types of dimensions that commonly used in AutoCAD and help you understand their differences. A good AutoCAD drawing will convey the needed information clearly and accurately. Dimensioning is used to let the drawing reader know what size each length or curve is, without having to open the drawing. If your dimensions are inaccurate, you will not be working in CAD for very long, no matter how accurate your drawing is. Learn when each dimension is needed and how to use it.

Dim Type Keystroke Icon Description
Linear DIMLINEAR / DIMLIN Dimensions for straight lines either horizontal or vertical to the UCS.
Aligned DIMALIGNED / DIMALI Dimensions for straight lines that are angled to the UCS and provides the line’s length.
Angular DIMANGLUAR / DIMANG Dimensions between 2 points and gives the resulting angle measurement.
Arc Length DIMARC Dimensions the length of an arc or arc segment of a polyline.
Radius DIMRADIUS / DIMRAD Dimensions the radius of an arc, circle or arc segment of a polyline.
Diameter DIMDIAMETER / DIMDIA Dimensions the diameter of an arc, circle or arc segment of a polyline.
Center Mark DIMCENTER Places a center mark at the center point of an arc or circle
Rotated

DIMROTATED

A modifier to a dimension to make it parallel to a selected line.
Align DIMSPACE Aligns the selected dimensions to an even spacing.
Continue DIMCONTINUE / DIMCONT Continues dimensioning from a base dimension
Baseline DIMBASELINE / DIMBASE Continues dimension from a base dimension to give an overall dim.

 

Types of Dimensions in AutoCAD

You have most likely already used some of the common dimension types like ‘linear’ or ‘radius’. This section will describe how each one works in mre detail.

Linear Dimensions:
Linear dimensions are used to create a dimension that measures a line that is either horizontal or perpendicular to the UCS. This is the most commonly used dimension and is very easy to use. Below is a typical linear dimension:

Linear Dimension in AutoCAD

It’s good practice (thought not always allowed by time) to have your dimensions at a consistent distance from the object. Make sure that it is not to close to overlap the object and not too far to confuse which object you dimensioned. To create a linear dimension, either use the icon or key in DIMLINEAR. Just pick the two endpoints of a line (or any two points) and then place the dimension line where you want it. Very quick, very simple.

Command: DIMLINEAR

Specify first extension line origin or <select object>:SELECT FIRST POINT
Specify second extension line origin:SELECT SECOND POINT
Specify dimension line location or
[Mtext/Text/Angle/Horizontal/Vertical/Rotated]: SELECT LOCATION OF DIM LINE
Dimension text = 5.00

Note that there are some options at the command line:

MText / Text You don’t need to use these, it doesn’t really affect your dimensionSE
Angle This will place your text at the angle you specify
Horizontal This will create a horizontal dim, but you select this when you place your dimension line. Rarely needed.
Vertical This will create a vertical dim, but you select this when you place your dimension line. Rarely needed.
Rotated This will create a ‘rotated’ dimension. This is explained below.

You’ll also notice on the first prompt, you can <select object>, Press <enter> at this point, and then you can just select the line instead of the two endpoints. This is a lot quicker and more accurate as you don’t have to worry about picking the wrong Osnap.

Aligned Dimensions:
The Aligned dimes ion works just like the linear dimension. The big difference is that it works with lines or distances that are not square to the UCS. You can also use this on any 2 points that are also compatible with the linear dimension. It will create a dimension parallel to the angled line.

Aligned Dimension in AutoCAD

Command: DIMALIGNED

Specify first extension line origin or <select object>:SELECT FIRST POINT
Specify second extension line origin:SELECT SECOND POINT
Specify dimension line location or
[Mtext/Text/Angle]: SELECT LOCATION OF DIM LINE
Dimension text = 2.00

You’ll see that command line prompts are almost the same. Of course, there are no option for horizontal or vertical placement. Also Rotate is missing to avoid confusion and errors. You can also select Angle for your text to match the angle of line (just select 2 points on the line you are dimensioning).

Angular Dimensions:
Not every dimension gives the reader a length. Sometimes other measurements are need. Angular dimensions will display the angle between two objects. The measurement of the angle is defined by your dimstyle, but degrees is standard. The command works similar to the linear dimensions (see a pattern?).

Angular dimension in AutoCAD

Command: _dimangular
Select arc, circle, line, or <specify vertex>: <select first line>
Select second line: <select second line>
Specify dimension arc

The example above shows 3 common uses of this tool. To get the angle on the arc, just select anywhere on it. Getting the outside measurement (225° in this example) is done by following the prompt <select vertex>.

Command: DIMANGULAR
Select arc, circle, line, or <specify vertex>:

Specify angle vertex: <select point A>
Specify first angle endpoint: <select point B>
Specify second angle endpoint: <select point C>
Specify dimension arc line location or [Mtext/Text/Angle/Quadrant]:<place dim>
Dimension text = 225

Angular dimension in AutoCAD


Arc Length:

This is a fairly new command in AutoCAD and will not be available on some older versions. This command works quite simply, just start the command and select an arc or arc segment of a polyline. In the example below, I have shown the Angular (180°) dimension with the Arc length so that you can see the difference. Notice the symbol in front of the 3.14.

Arc Length in AutoCAD

Command: _dimarc
Select arc or polyline arc segment: <select the arc>
Specify arc length dimension location, or [Mtext/Text/Angle/Partial/Leader]: 1.2
Dimension text = 3.14

Once again, you are offered some options when dimensioning. Mtext/Text/Angle are the same options for text that you saw earlier. Partialwill allow you to dimension only part of the arc. This is useful for midpoints or nodes, when the arc is segmented. Leader will draw a leader from the dim text to the arc that it refers to.

Arc Length in AutoCAD

Radius Dimension:
Another common and simple command. DIMRAD will dimension any arc or circle and give you the radius and place a center mark at the center of the selected object. A center mark is a cross the indicates the center point of an arc or circle.

Radius Dimension in AutoCAD

Command: _dimradius
Select arc or circle: <select object>
Dimension text = 0.40
Specify dimension line location or [Mtext/Text/Angle]: <place the dim>

Once again, you have some options for the text at the command prompt.

Diameter Dimension:
The diameter and radius dimensions work the same, but give a different measurement. As a rule, I will use the diameter dim on things like a hole to be drilled or for the dimensions of an overall part and radius for filleted corners, etc.

Diameter Dimension in AutoCAD

As you see, the diameter and radius dimensions add a center mark (this can be turned off, or changed to a larger line in DDIM). I will usually dimension the circles first so that I can select the center mark and have a small gap (it looks cleaner).

Command: _dimdiameter
Select arc or circle: <select the object>
Dimension text = 1.00
Specify dimension line location or [Mtext/Text/Angle]: <place the dim>

In the example image above, you can see that even a very simple drawing can have enough dimensions to clutter things up. Make sure that you have enough dimensions and don’t duplicate or miss any. Make sure that they can be read from one or two angles when printed (usually from the bottom right corner).

Center Mark:
By now you should be getting the hang of how this works. The center mark command adds a center mark to a circle or arc. How it is displayed is set in theDDIM dialog box under the “Symbols and Arrows” tab. If you select “None” you will not be able to place a center mark using this command. The icon for center marks is in the sub menu on the dimension panel.

Center Mark in AutoCAD

Sometimes you might use both in the drawing. Below. on the left, I used the center mark that was made with the diameter dimension, then I dimensioned from it. On the right, I used a Line center mark and extended one of the lines to the other side to indicate the the holes are aligned. Then I double-clicked on the diameter text and added a suffix to indicate that both holes are the same size.

Center Mark in AutoCAD

But when you do this, any of the center marks made by the diameter or radius dimensions will change to the new style that you selected. It’s best to start with one style and leave it.

Rotated Dimensions:
A rotated dimension is not a dimension that was rotated using the rotate command. Instead it allows you to create a linear dimension to two points that are not in a straight line. Look at the image below and see the difference between an aligned dimension and a rotated one.

Center Mark in AutoCAD

First, look the dimension on the far right. See how it gives a true overall size of 10 units? On the right, the aligned dimension is not the overall size due to the 94° angle in the bottom left corner. Also in the top right, notice the rotated dimension with 2.00 units. I need to rotate it as the 2 points that I selected were not on the same axis. A little confusing at first, but try it a few times.

Command: dimlin
DIMLINEAR
Specify first extension line origin or <select object>: <first endpoint>
Specify second extension line origin: <first endpoint>
Specify dimension line location or
[Mtext/Text/Angle/Horizontal/Vertical/Rotated]: R <enter>

Specify angle of dimension line <0>: <select first point on axis>
Specify second point: <select second point on axis>
Specify dimension line location or
[Mtext/Text/Angle/Horizontal/Vertical/Rotated]: <place dim>
Dimension text = 2.00

When it comes to selecting points on the axis, pick the common parallel line (in this example, I click 2 points on the 10 unit dimension. You can also created a rotated dim by using the DIMROTATED command. In this case, you select the angle first.

Align Dimensions:
Sometimes you might have a bunch of dimensions in one area and want to space them evenly. The easy way to do this is to place them quickly, then use the Align Dimension command, DIMSPACE. Look at the image below with the random spacing.  The image next to it shows what it looks like when “dimspace” is used correctly.

DIMSPACE in AutoCAD===>>>>>

Draw a similar shape and try this. Place your dims, but allow for enough room to fit them all (just don’t worry about the spacing). Then start theDIMSPACE command.

Command: DIMSPACE
Select base dimension: <I selected the 2.00 dim in this example>
Select dimensions to space:
Specify opposite corner: 3 found <select the others>
Select dimensions to space: <enter>
Enter value or [Auto] <Auto>: <enter>

Fast and easy. You have the option at the end to enter a distance between each dim, but Auto should work in most cases.

Continue Dimensions:
Another shortcut is to use continued dimensions. With this command, you can select a ‘base’ dimension and then have AutoCAD help by continuing the command so that you can just click and endpoint and continue to the next, click an endpoint, etc. Have a look at the drawing below:

Dimspace in AutoCAD

When you have a series of dimensions all in one plane like this, just create the first one with DIMLIN and then use the DIMCONT command to create the rest of them. In this example, I created the dim on the left first.

Tip: When using this command or the Baseline dimensions, select your points for the base dim in the direction that the others will follow. In the example above, since I selected the base dim on the left, I had to first pick the left point and then the right point. This sets the direction for the others to follow.

With the the DIMCONT command running, just select the next points to the right (A and the B in this example). After doing this, the next time you start theDIMCONT command, it will return to this point and continue on. Try this out in your own drawing with a simple shape like the one above.

Baseline Dimensions
This command is very similar in function to the continue command, but instead provides an overall dimension based upon the first point you select in your first (base) linear dimension.

Dimspace in AutoCAD

Once again, I first needed to create a base dimension with the DIMLIN command. I again used the dim on the left. Then I started the DIMBASEcommand and selected points A and B. Once again, try it out and see how this works. See what happens when you create your base dim from right to left.

Summary:
You have a lot of tools at your disposal when it comes to dimensions. The trick is to know when to use each one. It’s also extremely important that you are accurate. Clicking on another dimension instead of a line’s endpoint can be a huge mistake – especially in mechanical drafting where tolerances are small. Review your dimensions before sending a drawing off to someone else, or printing it- then check it again. Check for overlaps or other confusing areas. The commands themselves are easy to use, but accuracy is critical.