If you need a clear, step-by-step guide to using the units shortcut in AutoCAD, this article explains what the command does, how to use it, why it may sometimes fail, alternative commands and methods, common errors and fixes, and practical tips for everyday work. The content is beginner-friendly and optimized for search engines, with examples and a helpful FAQ.
What is the units shortcut?
The AutoCAD units shortcut is the quick command for opening the Drawing Units dialog. You can type UN (or the full command UNITS) at the command line to open this dialog. The UNITS command controls how AutoCAD displays length and angle formats and their precision, and how objects from other drawings are scaled on insertion.
Key points:
- UN / UNITS opens the Drawing Units dialog.
- It affects display formats (Decimal, Architectural, Engineering, Fractional, Scientific) and angle types (Degrees, DMS, Radians, Grads, Surveyor).
- It sets the insertion units used to scale blocks and Xrefs automatically.
- It does not automatically convert the actual size of existing geometry when you change the display units.
How to use the units shortcut (Step by step)
Using the command line
- Press the command line and type UN or UNITS, then press Enter. (Use an underscore: _UNITS to ensure the command works in different language versions of AutoCAD.)
- The Drawing Units dialog opens.
- Under Length, choose a Type: Decimal, Engineering, Architectural, Fractional, or Scientific.
- Set Precision for length (number of decimal places or fractional resolution).
- Under Angle, choose an Angle Type: Decimal Degrees, Deg/Min/Sec, Grads, Radians, Surveyor’s Units.
- Set angle precision (decimal places or DMS precision).
- Under Insertion scale, choose the drawing unit for objects inserted from other drawings (e.g., Inches, Millimeters, Meters).
- Click OK to apply changes.
Using the Ribbon / Menus
- Application Menu > Drawing Utilities > Units
- Or Format menu (older versions) > Units
- Or right-click Model tab > Drawing Utilities > Units
Important options explained
- Length Type: Determines how linear measurements are displayed (e.g., Decimal for meters, Architectural for feet-inches).
- Length Precision: Controls the number of decimal places or fraction precision displayed.
- Angle Type and Angle Precision: Controls angle display format and rounding.
- Insertion scale: Defines the unit used when inserting blocks/Xrefs. Proper setting avoids unwanted scaling.
- Rotation (zero angle): In some versions you can set the default rotation for angle display.
Examples and practical scenarios
Example 1 — Display-only change (Decimal to Architectural)
- Situation: A plan was drawn using metric coordinates but you want dimensions shown as feet and inches.
- Steps: Type UN → Length Type = Architectural → set Precision → OK.
- Result: Display and dimension formatting change (if dimension style uses drawing units), but the geometry size in Model space is unchanged.
Example 2 — Converting a drawing from inches to millimeters (real conversion)
- Important: Changing UNITS alone will NOT convert object sizes. To convert geometry:
- Determine the conversion factor (1 inch = 25.4 mm).
- Select all objects (CTRL+A).
- Use the SCALE command, pick a base point (0,0 recommended), enter the factor (25.4) to scale geometry to millimeters.
- Then set UN → Insertion scale and Length Type to Decimal / Millimeters.
- Result: Geometry is now correctly scaled to millimeters and displays in chosen units.
Example 3 — Fixing block insertion scale mismatches
- If a block created in inches inserts too large in a mm drawing:
- Set the block’s source drawing insertion units before saving, or
- Use -INSERT with a scale factor, or
- Change INSUNITS (system variable) or the destination drawing’s Insertion scale so AutoCAD auto-scales block on insertion.
Why the units shortcut sometimes doesn’t work (errors and fixes)
Symptom: Typing UN or UNITS does nothing or returns “Unknown command.”
- Fixes:
- Try the full command UNITS or add an underscore _UNITS.
- Check the command aliases file (acad.pgp) — the alias for UN may have been removed or altered.
- Ensure you are not in a special command mode (press Esc) and try again.
Symptom: Changing units doesn’t change dimension labels or measurement output
- Causes & fixes:
- Dimensions use their own settings (Dimension Style Manager). Open DIMSTYLE and check Primary Units format and precision.
- Some measurement commands use system variables like LUNITS, LUPREC or dimension scale factors (DIMLFAC). Check and adjust these.
- After changing units, run REGEN or regenerate the drawing to refresh display.
Symptom: Inserting drawings or blocks are scaled incorrectly
- Causes & fixes:
- Check Insertion scale in both drawings. Use UN to confirm, and set appropriate INSUNITS values.
- When inserting with the Insert dialog, ensure “Specify On-screen” options are handled correctly.
- If automatic scaling is not desired, use -INSERT and set the scale manually or set insertion units to Unitless.
Symptom: Display looks wrong or values appear truncated
- Fixes:
- Increase Precision in the Drawing Units dialog.
- Check dimension style rounding or use higher precision in DIMSTYLE.
Symptom: UNITS command opens but settings revert after closing
- Fixes:
- Save the drawing and confirm profile settings. Check for custom scripts or LISP that reset units on file open.
- If problem persists across drawings, reset AutoCAD to default profile or repair installation.
Alternative methods and related commands
- _UNITS — Use underscore for language-independent access.
- INSUNITS — System variable that stores insertion units; check/set with the command line: type INSUNITS and enter a number or use the dialog.
- DIMSTYLE — Control dimension display, units, and precision separately from UNITS.
- SCALE — Scale geometry when you need to convert actual object sizes between unit systems.
- -INSERT — Command-line insertion that allows explicit scale factors when inserting blocks (useful for unit conversion).
- AUDIT / RECOVER — Use if a corrupted drawing causes commands to misbehave.
- acad.pgp — Edit this file to restore or add command aliases (advanced).
- Drawing Templates (.dwt) — Set your preferred UNITS in a template so new drawings start with the correct units.
Tips & best practices
- Use _UNITS to ensure compatibility across localized AutoCAD versions.
- Remember: changing UNITS only changes display, not actual geometry. Use SCALE for conversions.
- Set Insertion scale correctly in both source and target drawings to avoid unwanted resizing of blocks and Xrefs.
- Keep consistent units across your project team: use a standard drawing template (.dwt) with units preset.
- Check DIMSTYLE if dimensions do not reflect the units format you set.
- Use REGEN after changing units or styles to refresh the view.
- When converting units, always keep a backup of the original file before scaling.
- Use clear layer and block naming conventions that include unit info (e.g., “Block_Arch_inch”) to avoid confusion.
FAQ
Does changing units with UNITS change the actual size of objects?
No. The UNITS command controls display format and insertion behavior. It does not scale or resize existing geometry. To change the actual size, use the SCALE command with the correct conversion factor.
Why does typing UN say “Unknown command”?
Either your acad.pgp alias file was modified and UN alias removed, or you need to use the full command (UNITS) or the language-independent form (_UNITS). Check that you’re not in another command (press Esc) and that command aliases are intact.
How do I convert a drawing from inches to millimeters properly?
After deciding the conversion factor (1 inch = 25.4 mm):
- Select all objects.
- Use SCALE, pick a base point (0,0 recommended), enter the factor (25.4).
- Then set UN to Millimeters (Insertion scale) and update dimension styles if necessary.
Why do dimensions still show the old units after I changed UNITS?
Dimensions use settings in DIMSTYLE. Open DIMSTYLE, check Primary Units format and precision, and ensure dimension scale factors aren’t overriding the display.
How do I ensure blocks insert at the correct size from other drawings?
Set the Insertion scale (UNITS) and check the INSUNITS of both drawings. If necessary, insert with -INSERT and specify a scaling factor, or re-save source blocks with the correct insertion units.
Can I set default units for all new drawings?
Yes. Create a drawing template (.dwt) with your preferred UNITS, dimension styles, and settings, then start new drawings from that template.
Is there a difference between UN and UNITS?
No functional difference — UN is the alias (shortcut) for the UNITS command. If UN fails, try UNITS or _UNITS.
What should I do if changing units has unexpected results or the command stops working?
Try REGEN, run AUDIT and RECOVER on the drawing, check for startup scripts or LISP routines that may reset settings, and restore or reset your AutoCAD profile if needed.