Linetypes in AutoCAD: loading them, writing your own, and the scale

Linetypes in AutoCAD are something everyone uses and almost nobody opens up. The result is two questions that come back forever: why a dashed line still draws as a solid one, and how to get a pipe run with letters marching along it.

This article opens the definition file, points at the one setting that matters, and includes a small library from the Institute to download. For the whole layer and linework workflow, see the AutoCAD for Construction course.

Where the patterns live: two files, 45 and 59 of them

Every pattern sits in a plain text file with a .lin extension. AutoCAD 2027 installs two of them, and we counted the definitions directly on the machine at the Institute:

Which one the program reaches for is decided by the MEASUREMENT variable. A value of 1 means metric. The proof appears in the prompt itself, where AutoCAD offers the file name as a default:

Enter name of linetype file to search <acadiso.lin>:

Both files sit in the Support folder of the user profile, at %APPDATA%\Autodesk\AutoCAD 2027\R26.0\enu\Support. Notepad opens them, because they are ordinary text.

Searching for a linetype library brings up a flood of downloads, most of them copies of the same .lin file. Before going looking, it is worth opening the two you already have, since they cover almost everything an architectural or structural sheet needs.

The distinction that trips people up is that linetypes in AutoCAD live in two places at once: in the definition file on disk, and in the drawing that has loaded them. Editing the file on disk changes nothing in drawings that already hold a copy of the pattern.

Worth noting: a new drawing holds only three. We checked an empty file and the list held ByBlock, ByLayer and Continuous. The other fifty-nine sit in the file, not in the drawing. They have to be loaded first, and that is where people conclude the software is missing something.

The Institute linetype library: six patterns, ready to download

The stock set lacks exactly the patterns Vietnamese infrastructure sheets need. We gathered six and sized them in millimetres, for drawings built in mm.

Download IIC.lin — 876 bytes, six patterns. The contents stay in the article, because it is a text file you can read in a minute.

;;  IIC.LIN - thu vien kieu duong cho ban ve xay dung
;;  Vien Tin hoc Xay dung (IIC) - Truong Dai hoc Xay dung Ha Noi
;;  https://iic.huce.edu.vn  -  Tel: 0989 427 809
;;
;;  So do theo MILIMET, hop voi ban ve dung don vi mm (INSUNITS = 4).
;;  Nap bang: LINETYPE -> Load -> tro toi tep nay -> chon kieu can dung.

*IIC_KHUAT,Net khuat __ __ __ __ __ __ __ __ __ __ __ __
A,8,-4

*IIC_TIM,Net tam ____ _ ____ _ ____ _ ____ _ ____ _ ____
A,20,-3,2,-3

*IIC_RANH,Ranh gioi ___ . ___ . ___ . ___ . ___ . ___ .
A,15,-3,0,-3

*IIC_CAPNUOC,Cap nuoc ----N----N----N----N----N----N----
A,12,-6,["N",STANDARD,S=2.5,U=0.0,X=-1.2,Y=-1.25],-6

*IIC_THOATNUOC,Thoat nuoc ---TN---TN---TN---TN---TN---
A,14,-8,["TN",STANDARD,S=2.5,U=0.0,X=-2.4,Y=-1.25],-8

*IIC_DIEN,Duong dien ----E----E----E----E----E----E----
A,12,-6,["E",STANDARD,S=2.5,U=0.0,X=-1.2,Y=-1.25],-6

Loading the library, step by step

Step 1 — Load the file into the drawing

1. Type LINETYPE and press Enter. The linetype manager opens.
2. Click Load... in the upper right.
3. In the dialog that opens, click File... and point at the IIC.lin you downloaded.
4. Select the patterns you want, or press Ctrl and A for all of them, then click OK.

The command line route is quicker. Type -LINETYPE and AutoCAD asks:

Enter an option [?/Create/Load/Set]:

Type L for Load. It asks which patterns, where an asterisk takes them all, and then for the file path. It confirms each one:

Linetype "IIC_KHUAT" loaded.

Step 2 — Assign the pattern

The tidy way is to assign it to a layer, not to individual objects. Open the layer manager, click the linetype column for that layer and pick. Every object on the layer then carries the right pattern. Our article on layers in AutoCAD covers that workflow. Assigning by layer has a second benefit: change it in one place and the whole sheet follows, instead of reselecting objects when the client asks for a different convention.

Step 3 — Set the scale so the pattern appears

This is the step people skip, and the reason most of them think the file is broken. There is no single right number: it follows the plot scale, so a detail at 1:20 and a site plan at 1:500 on the same set will want different values, which is one argument for keeping each scale on its own sheet. Type LTSCALE, enter a number and press Enter. A millimetre drawing plotted at 1:100 usually wants something between 20 and 50.

A dashed line not showing is almost always the scale

The LTSCALE page at Autodesk describes the variable in one line: "Sets the global linetype scale factor". Type Real, saved in the drawing, initial value 1.0000.

That number multiplies every distance in the definition. IIC_CAPNUOC has a 12 mm dash and a 6 mm gap. At a factor of 1 the whole cycle is 36 mm along a line four metres long, so the eye reads it as solid. At 20 the cycle becomes 720 mm and it reads immediately.

Three variables act at once, so it is worth separating them. LTSCALE multiplies the whole drawing. CELTSCALE multiplies again, for the object about to be drawn, and the two are multiplied together. PSLTSCALE only matters when printing through a layout. For daily work you only ever touch the first.

Writing a custom linetype: read one line and you can do it

Each pattern takes exactly two lines. The first carries the name and a description, the second the definition. Here is DASHED, copied verbatim from acadiso.lin on the machine:

*DASHED,Dashed __ __ __ __ __ __ __ __ __ __ __ __ __ _

A, 12.7, -6.35

Read the second line: A is the required alignment code, 12.7 is a dash 12.7 units long, -6.35 is a gap of 6.35 units. That is all of it. Positive is a dash, negative is a gap, zero is a dot.

A pattern with text adds a pair of square brackets. Here is GAS_LINE, also verbatim:

A,12.7,-5.08,["GAS",STANDARD,S=2.54,U=0.0,X=-2.54,Y=-1.27],-6.35

Inside the brackets come the text, the text style used to draw it, S for size, and X and Y to shift the letters into the gap. Autodesk's About Simple Custom Linetypes sets two limits: "A description cannot exceed 47 characters", and no more than 12 numbers per pattern.

Once you can read that, writing linetypes in AutoCAD becomes a five minute job rather than a search for someone else's file.

Save the result as a .lin file and load it as above. No restart needed.

One caution when picking your own numbers: they are in drawing units, not millimetres on paper. Copy the figures out of acadiso.lin into a drawing built in metres and the cycle becomes tens of metres long. That is why the Institute ships a separate file for millimetre drawings rather than telling you to edit the one the software installed. For automation beyond this, see our article on a lisp that shortens extension lines.

MKLTYPE: draw a sample and let AutoCAD write the definition

If counting numbers is not your idea of fun, there is another route. Draw a line and a piece of text exactly as you want the pattern to look, then type MKLTYPE. AutoCAD answers:

Initializing...

and opens a MKLTYPE - Select Linetype File dialog for you to choose where to save. It then asks for a name, a description, the two ends of one cycle, and finally for the objects to copy. Out comes a finished .lin file.

We typed it on AutoCAD 2027 and the command ran normally. It belongs to the Express Tools set, so an installation without that set will not have it.

Three things often repeated that are not true

Frequently asked questions

I loaded the pattern and the line is still solid. Why?

Check LTSCALE first. On a millimetre drawing left at 1, the cycle is a few tens of millimetres, which reads as solid at sheet zoom. Try 20 and adjust from there.

Where should a downloaded library file live?

Next to the drawing set is fine, because once loaded the definitions live inside the drawing. For long-term use, copy it into the Support folder so you do not go hunting next time.

Do I have to send the .lin file with the drawing?

No. Loaded patterns are stored in the DWG itself. The source file is only needed if the recipient wants to load further patterns.

How do I remove patterns I am not using?

Type PURGE, pick the linetypes group and delete. Anything still in use is kept, so nothing on the sheet can break.

Can one object have its own scale?

Select it and edit the Linetype scale box in the Properties palette. That figure multiplies with LTSCALE rather than replacing it, so count both.

Can I name a pattern with accented characters?

Better not. Names travel with the drawing across machines and releases, and accents are the first thing to break. The Institute library uses plain letters for that reason.