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How to Change Units in AutoCAD

Setting the correct drawing units in AutoCAD is important for accurate design, drafting, dimensioning, and documentation. AutoCAD allows you to specify how distances and angles are interpreted and displayed.

The UNITS command is commonly used to configure the drawing’s unit settings. However, an important point to remember is that changing the UNITS settings does not automatically resize existing geometry.

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1. Use the UNITS Command

The easiest way to configure AutoCAD drawing units is with the UNITS command.

Step 1: Open the Units Dialog Box

UNITS

in the command line and press Enter.

The Drawing Units dialog box will open.

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Step 2: Set the Length Type

Under Length, select the appropriate type.

Common options include:

• Decimal
• Architectural
• Engineering
• Fractional
• Scientific

For most engineering drawings, Decimal is commonly used.

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Step 3: Set the Precision

Choose the number of decimal places you want AutoCAD to display.

For example:

• 0
• 0.0
• 0.00
• 0.000

The precision controls how values are displayed, not the physical size of the geometry.

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Step 4: Set the Angle Type

Under Angle, select the required format.

Common options include:

• Decimal Degrees
• Degrees/Minutes/Seconds
• Grads
• Radians
• Surveyor’s Units

For many engineering workflows:

Decimal Degrees

is a convenient choice.

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Step 5: Set Insertion Scale

The Insertion Scale setting controls how objects created in one drawing are interpreted when inserted into another drawing with different unit settings.

Common choices include:

• Millimeters
• Centimeters
• Meters
• Inches
• Feet
• Unitless

For example, if you are working on a mechanical drawing in millimeters, select:

Millimeters

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Step 6: Click OK

After configuring the settings, click:

OK

Your drawing’s unit-display and insertion settings are now configured.

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2. Common AutoCAD Units

Different industries commonly use different units.

Millimeters (mm)

Widely used for:

• Mechanical drawings
• Manufacturing
• Engineering
• Architectural details
• MEP drawings

Example:

500 mm

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Meters (m)

Commonly used for:

• Civil engineering
• Site plans
• Large buildings
• Infrastructure projects
• Land development

Example:

25 m

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Centimeters (cm)

Used in some architectural, design, and technical workflows.

Example:

50 cm

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Inches (in)

Common in:

• US engineering
• Manufacturing
• Architectural drawings
• Mechanical design

Example:

12 in

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Feet (ft)

Common in:

• US construction
• Architecture
• Civil engineering
• Building plans

Example:

20 ft

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3. Important: UNITS Does Not Scale Existing Geometry

This is one of the most important things to understand about AutoCAD units.

Changing the setting in:

UNITS

does not automatically make existing geometry larger or smaller.

For example, suppose you have a line whose AutoCAD length is:

100

If you change the drawing’s unit setting from millimeters to meters, the line does not automatically become 1000 mm or 0.1 m.

The geometry itself remains the same size in drawing coordinates.

UNITS controls:

• How units are interpreted
• How values are displayed
• Insertion-unit behavior

UNITS does not:

• Automatically resize existing geometry
• Convert all existing dimensions
• Change the coordinates of your objects

Common Unit Conversion Scale Factors

Conversion	Scale Factor
mm → m	0.001
m → mm	1000
cm → m	0.01
m → cm	100
in → ft	0.0833333
ft → in	12

These factors are used when you need to physically convert existing geometry, rather than merely change the unit settings.

Autodesk Support: How to Convert Drawing Units Within a File: Direct instructions for converting between units (e.g., millimeters to meters) and matching INSUNITS to active drawing units.

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Best Practices

1. Decide Units Before Starting

For a new project, establish whether you will work in:

mm, cm, m, inches, or feet

before creating significant geometry.

2. Check Units When Receiving Drawings

Always verify the units of external DWG files before combining them with your drawing.

3. Verify a Known Dimension

Use DIST or the Properties palette to check a known dimension before scaling an existing drawing.

4. Use Templates

Create project templates with the correct units, layers, styles, and other CAD standards already configured.

5. Be Careful With Xrefs and Blocks

Different drawings can use different unit settings. Incorrect insertion-unit configuration can cause blocks or external references to appear at the wrong size.

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Frequently Asked Questions (FAQs)

1. What command changes units in AutoCAD?

Use the:

UNITS

command.

2. Does changing UNITS resize my drawing?

No. The UNITS command changes unit settings and interpretation; it does not automatically scale existing geometry.

3. How do I convert an existing drawing from meters to millimeters?

Use SCALE with a factor of 1000, then configure the appropriate unit settings.

4. How do I convert millimeters to meters?

Use SCALE with a factor of 0.001.

5. Which unit is commonly used in mechanical AutoCAD drawings?

Millimeters are commonly used in many mechanical and manufacturing workflows.

6. Which units are commonly used in civil drawings?

Depending on the project and regional standards, meters, millimeters, feet, or inches may be used.

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Conclusion

Changing units in AutoCAD is a two-part concept:

Configure Units

UNITS → Set Length/Angle → Set Insertion Scale → OK

Convert Existing Geometry

SCALE → Select Objects → Base Point → Enter Conversion Factor

The key point is:

UNITS changes how AutoCAD interprets and displays units; SCALE changes the actual size of existing geometry.

Always verify a known dimension after converting a drawing to ensure that the geometry is at the intended scale.

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