How to Lock Dimension in AutoCAD? (Step by step)

Locking dimensions in AutoCAD ensures the consistency and accuracy of your design measurements even if the geometry changes. This is essential for maintaining precise specifications in your drawings. There are several methods to lock dimensions, each serving a different purpose. Let’s explore these methods in detail.

Method 1: Locking Dimension Value

Locking the dimension value prevents the numerical value from changing, even if the objects it measures are modified. This is useful when the dimension itself is more critical than the geometry it measures.

Steps to Lock Dimension Value:

1. Select the Dimension:
   • Click on the dimension you wish to lock. This will highlight the dimension and display its properties in the Properties palette.
2. Open the Properties Palette:
   • If the Properties palette is not already open, type PROPERTIES in the command line and press Enter. Alternatively, you can press CTRL + 1 to open the Properties palette.
3. Lock the Dimension:
   • In the Properties palette, scroll down to the section labeled Misc.
   • Find the property labeled “Lock.” By default, it is set to “No.”
   • Click on the value next to “Lock” and change it to “Yes.”
4. Verify the Dimension is Locked:
   • Test the locked dimension by attempting to modify the geometry it measures. The dimension should remain unchanged, indicating it is locked.

Method 2: Locking Dimension Annotativity

Locking dimension annotativity ensures that the dimension’s size remains consistent when you change the drawing scale. This is especially useful for keeping dimensions readable in different layouts.

Steps to Lock Dimension Annotativity:

1. Open the Dimension Style Manager:
   • Type DIMSTYLE in the command line and press Enter to open the Dimension Style Manager.
2. Select the Dimension Style:
   • Select the dimension style you are using from the list.
3. Modify the Dimension Style:
   • Click “Modify” to open the Modify Dimension Style window.
4. Enable Annotative Scaling:
   • Go to the “Fit” tab.
   • Under “Scale for Dimension Features,” check the “Annotative” box.
   • Click “OK” to apply the changes and close all windows.

Method 3: Using Constraints (More Advanced)

Constraints offer greater control over dimension locking. You can apply dimensional constraints to lock distances, angles, and relationships between objects. This method provides advanced control over your dimensions.

Steps to Apply Dimensional Constraints:

1. Select the Geometry:
   • Select the geometry you want to dimension.
2. Apply Constraints:
   • Use the PARAMETRIC tab or type the specific constraint command (e.g., DIMCONSTRAINT, ANGCONSTRAINT) to apply the desired constraint.

Important Considerations

Overriding Locks:

If you need to modify a locked dimension, you can temporarily unlock it by changing the “Lock” property back to “No” or by removing the constraint.

Annotative Scales:

For annotative dimensions, ensure you set appropriate scales in your layout viewports to control how the dimension appears.

Using DIMLOCKED System Variable:

You can use the DIMLOCKED system variable to lock and unlock dimensions globally. Type DIMLOCKED in the command line and set it to 1 to lock all dimensions in the drawing. Set it to 0 to unlock them.

Layer Control:

Consider placing locked dimensions on a specific layer. You can then lock or freeze that layer to prevent any changes to those dimensions.

Example Command: