Where to find the units setting in AutoCAD

Open AutoCAD and go to the process Menu (the red "A" in the top left corner). Click it, then select Drawing Utilities, then Units. A dialog box titled "Drawing Units" will open. This is where you change what measurement system your drawing uses — inches, millimeters, feet, centimeters, or others.

If you cannot find the process Menu, you can also type UNITS directly into the command line at the bottom of the screen and press Enter. The same dialog box will appear. Either method works; use whichever feels faster to you.

Key Takeaways

  • The Drawing Units dialog opens through the process Menu under Drawing Utilities, or by typing UNITS into the command line.
  • The Length dropdown controls what unit name appears next to your dimensions — inches, millimeters, feet, or centimeters.
  • Changing units does not rescale your drawing; a line that was 10 units long stays 10 units long, but the label changes from "10 inches" to "10 millimeters" or whatever you select.
  • If you need your drawing to actually change size (a 10-inch line become a 10-millimeter line), you must scale the geometry itself, not just the unit label.
  • Set units before you start drawing, because changing them mid-project can create confusion about what dimensions actually mean.

Selecting a new unit type from the dropdown

In the Drawing Units dialog, look for the Length section. You will see a dropdown menu that currently shows your active unit — probably "Decimal" or "Architectural". Click that dropdown to see all available options: Decimal (generic), Architectural (feet and inches), Engineering (feet and decimal inches), Fractional (inches as fractions), and Scientific (for very large or very small numbers).

Choose the one that matches how you want dimensions to display. If you are working in millimeters, select Decimal and then change the unit label in the next step. If you are working in feet and inches the way architects do, select Architectural. The dropdown changes the format of how numbers appear, not the actual measurement system yet.

Setting the unit label and precision

Below the Length dropdown, you will see another field labeled Precision. This controls how many decimal places show up in your dimensions. If you set it to 0.00, dimensions will show two decimal places (like 10.50). If you set it to 0.0000, they will show four decimal places (like 10.5000). Choose based on how precise your work needs to be — architectural drawings often use 0.00, while mechanical drawings might use 0.0000.

To the right of the Length dropdown, you may see a unit label field (this varies by AutoCAD version). If present, you can type in what you want the unit called — "mm" for millimeters, "in" for inches, or anything else. This label appears in dimension text so anyone reading the drawing knows what measurement system you are using.

Understanding what changing units actually does

This is the most important thing to understand: changing the unit label does not resize your geometry. If you draw a line 10 units long, then change the units from inches to millimeters, that line is still 10 units long — but now it is called 10 millimeters instead of 10 inches. The line itself does not shrink. This is why setting units before you start drawing matters so much.

If you need your drawing to actually change size — to convert a 10-inch line into a 10-millimeter line — you must use the Scale command. Type SCALE into the command line, select all your geometry, and enter a scale factor. The math depends on your conversion: to go from inches to millimeters, multiply by 25.4. But most of the time, you just want to change the label, not the size, so leave your geometry alone.

explore the change and closing the dialog

Once you have selected your unit type and precision, click the OK button at the bottom of the Drawing Units dialog. The dialog closes and your drawing now uses the new unit system. Any new dimensions you add will display in the unit you selected. Existing dimensions will also update to show the new unit label.

If you made a mistake and want to undo the change, press Ctrl+Z when ready, or go back to the Drawing Units dialog and select the previous unit. There is no penalty for changing units multiple times — just remember that your geometry size does not change, only the label.

Changing units for an existing drawing from another source

If someone sends you a drawing and you are not sure what units it uses, open it and check the Drawing Units dialog. Look at the Length setting and the Precision. If the drawing was created in inches but you need it in millimeters, you have two choices: change the label only (if the numbers happen to work out), or scale the entire drawing by 25.4 to make it physically larger.

Before you scale, ask yourself: does the drawing need to be physically bigger, or do I just need to understand what the numbers mean? If a drawing shows a 10-unit line and was made in inches, that line is 10 inches. If you change the label to millimeters without scaling, it becomes 10 millimeters — much smaller. Scale only if the physical size matters for your project. If you are just reading dimensions, changing the label is enough.

Setting up units for different drawing types

Architectural drawings typically use feet and inches, so select the Architectural format and set precision to 0.00 or 0.0 (depending on how detailed your work is). Engineering drawings often use decimal feet or inches, so select Decimal and set precision to 0.0000. Mechanical and product design drawings usually work in millimeters, so select Decimal, set precision to 0.00, and label the unit as "mm".

If you work on the same type of drawing repeatedly, you can save your unit settings as part of a template. Create a blank drawing with your preferred units, dimensions style, and layers, then save it as a template file. Every new drawing you start from that template will already have the correct units, saving you the step of changing them each time.

Frequently Asked Questions

Will changing units affect dimensions I already drew?

The dimension values will update to show the new unit label, but the geometry itself does not change size. A line that was 10 inches stays the same physical length — it just now says 10 millimeters. If you need the line to actually become smaller or larger, use the Scale command instead.

What is the difference between Decimal and Architectural format?

Decimal shows measurements as plain numbers (10.50). Architectural shows feet and inches the way builders write them (10'-6", meaning 10 feet 6 inches). Choose Decimal for most mechanical work and Architectural for building and construction drawings.

Can I change units in the middle of a project?

Technically yes, but it creates confusion. If you change units halfway through, old dimensions will show the new label but the geometry stays the same size, so the numbers no longer match reality. Set units before you start drawing, or scale your entire drawing if you must switch systems mid-project.

How do I know what units a drawing was made in?

Open the Drawing Units dialog and look at the Length setting and the numbers in your dimensions. If a line shows 10.00 and looks very small on screen, it was probably made in millimeters. If it looks large, it was probably made in inches. You can also ask whoever created the drawing or check any notes in the title block.

What does precision do, and how precise do I need to be?

Precision controls how many decimal places appear in dimensions. Architectural work usually needs 0.00 (two decimal places). Mechanical work often needs 0.0000 (four decimal places) for tighter tolerances. Set it based on how exact your design needs to be — more decimal places do not make a drawing better, just harder to read if you do not need that detail.