Dimensioning: Free AutoCAD Tutorial
Master AutoCAD Dimensioning Tools and Professional Drawing Standards
Dimensioning is critical for technical drawings as it provides precise measurements and manufacturing specifications that ensure proper construction and assembly.
Key Learning Areas
Dimensioning Tools
Master the complete set of AutoCAD dimensioning tools including linear, aligned, angular, and radial dimensions with their keyboard shortcuts.
Mechanical Dimensions
Learn specialized tools for technical drawings including centerlines, centermarks, and proper dimensioning for mechanical components.
Dimension Editing
Understand how to modify dimension styles, precision, text positioning, and resolve overlapping dimension lines professionally.
Exercise Preview
Dimensioning tools are accessible from three locations: Dimension Toolbar, Annotation Panel on Home tab, or Dimension Panel in Annotate tab for maximum workflow flexibility.
Essential Dimension Commands
Linear Dimensions
DLI command creates horizontal and vertical dimensions. Works orthographically for precise rectangular measurements on technical drawings.
Aligned Dimensions
DAL command dimensions angled edges by aligning with the slope of the line, perfect for non-orthogonal geometry.
Radial Dimensions
DRA and DDI commands handle radius and diameter measurements for circular features with automatic center mark placement.
Angular Dimensions
DAN command measures angles between two line segments, essential for mechanical drawings with precise angular requirements.
Most dimensioning commands follow the formula: D + first two letters of the tool name (e.g., Linear = DLI, Aligned = DAL, Angular = DAN).
Mechanical Dimension Tools
Now we'll apply these tools in a real-world mechanical drawing scenario, demonstrating proper dimensioning practices that meet industry standards.
Open the file Dimensions-Manifold Brace.dwg. This technical drawing represents a typical mechanical component requiring comprehensive dimensional annotation.
Switch to the C-Sized Layout and enter Model Space. Change the current layer to Centerlines. This layer organization follows industry best practices for maintaining clean, readable technical drawings.
In the front view at the bottom of the viewport, you'll notice dashed lines representing hidden edges of circular holes. Professional drafting standards require centerlines in this situation to clearly indicate that holes are circular and show where center points align across multiple views. The Centerline tool automates this critical annotation process.
Initiate the Centerline tool by pressing the Centerline button or typing Centerline ENTER. Click on the first two dashed hidden lines from the right—a centerline will automatically appear between them. Restart the tool and systematically click on the remaining hidden lines to create centerlines between each pair. This methodical approach ensures consistent centerline placement throughout your drawing.
Switch to Paper Space. Type DLI ENTER to activate the Linear Dimensioning tool. Here's a key AutoCAD advantage: even while working in Paper Space, the dimensioning tools intelligently snap to model geometry and measure actual object dimensions, streamlining the annotation process.
Focus on the front view at the bottom of the viewport. Snap and click on both corners of the object's right side as illustrated below. AutoCAD creates a linear dimension in Paper Space that remains linked to the model geometry. Pull the dimension to the right and type 1 ENTER to position the dimension line exactly 1 inch from the object in Paper Space—this consistent offset creates professional-looking drawings.
Return to Model Space to explore AutoCAD's powerful associative dimensioning feature. This intelligent system links dimensions directly to the geometry they measure, automatically updating measurements when objects change—a crucial capability for design iterations and revisions.
Select the line segment at the right edge of your dimensioned object. Click the top grip and extend the line upward, then select the top edge line, click its right grip, and connect it to the extended line's top. Watch as the geometry changes—the linear dimension dynamically follows the modifications and updates its displayed measurement in real-time. This associative behavior prevents the dimensional errors that plague static annotation systems. Use Undo to restore the original geometry.
Apply the Linear Dimension tool to dimension the object's bottom edge as shown below. Remember to enter a distance of 1 when positioning the dimension lines. You'll notice the dimension lines intersect with the title block—a common layout challenge we'll resolve in the next step using professional repositioning techniques.
Professional drawings require clear separation between dimensions and title blocks. Switch to Model Space and unlock the viewport to enable model repositioning. Use the mouse wheel to pan the model leftward until the right edge positions slightly left of the title block, as shown below. Maintain adequate space on the left side for future dimensions. Notice that Paper Space dimensions remain stationary during this repositioning—we'll synchronize them in the next step.
Type DIMREGEN and press ENTER to execute the dimension regeneration command. This powerful command recalculates dimension positioning to match the model's new location, maintaining proper associative relationships. Occasionally, you may need to fine-tune dimension placement manually using grips after running DIMREGEN—this hybrid approach of automated positioning with manual refinement ensures optimal results. Lock the viewport and return to Paper Space to continue dimensioning.
Apply the Linear Dimension tool to the leftmost edge of the front view, maintaining the standard 1-inch offset from the object as shown below. This dimension will serve as the baseline for advanced dimensioning techniques we'll explore shortly.
Understanding tool limitations enhances your dimensioning strategy. The Linear Dimension tool operates orthographically, creating only vertical or horizontal dimensions. For angled features, the Aligned Dimension tool provides the solution by measuring true lengths along inclined edges.
Type DAL ENTER to activate the Aligned Dimension tool. Snap to each endpoint of the angled edge in the top view, pull outward from the object, and type 1 ENTER to maintain consistent dimension line offset as demonstrated below. This tool automatically calculates the true length of the angled edge, regardless of its orientation.
Angular relationships require specialized dimensioning. Type DAN ENTER to start the Angular Dimension tool. Unlike linear tools that rely on endpoints, this tool analyzes entire line segments to determine angular relationships. Click on the angled line you just dimensioned with the Aligned Dimension tool, then click the connected angled line at the top of the first line. Pull the dimension to the right, positioning it within available space. In constrained areas like this, prioritize clarity over rigid offset standards.
Circular features require specific dimensioning approaches. Type DRA ENTER to activate the Radius Dimension tool. Click on the inner circle from the concentric circle pair in the lower left corner and type 1 ENTER for automatic positioning with proper offset. AutoCAD intelligently places a center mark within the circle, following technical drawing standards that aid in manufacturing and inspection processes.
Diameter dimensions serve different manufacturing requirements than radius dimensions. Type DDI ENTER to start the Diameter Dimension tool. Click on the outer circle from the upper left concentric pair and type 1 ENTER for consistent positioning. Again, AutoCAD automatically adds a center mark, maintaining professional annotation standards throughout your drawing.
Center marks and centerlines communicate crucial manufacturing information by showing hole alignments and center point relationships across multiple views. This step systematically adds center marks to all circular features.
Change the Current Layer to Centerline to maintain proper layer organization. Type CENTERMARK ENTER or press the Centermark tool button in the Centerlines Panel on the Annotate Ribbon tab. Methodically click on all 5 inner circles in the top view to add center marks to each circle. Press Enter or Esc to exit the tool. These center marks will enable the creation of alignment centerlines in subsequent steps.
Centerline connections visually communicate hole alignment relationships critical for manufacturing accuracy. Select the centermark in the lower left corner, then click on its right grip and drag it rightward until it snaps to the left Endpoint of the adjacent centermark. AutoCAD automatically creates a Centerline connection, clearly indicating that these two circles share horizontal alignment—essential information for machining operations.
Complete the centerline network by repeating this connection process for the bottom right, top right, and top left Centermarks as shown below. This systematic approach creates a comprehensive alignment map that guides manufacturing processes and quality control inspections.
Return to dimensioning by changing the Current Layer to Dimensions. Type DLI to restart the Linear Dimension tool. Create linear dimensions between the bottom endpoint of the lower left center mark and the object's lower left endpoint. Click the Centermark first—this sequence ensures that when you enter the 1-inch dimension line offset, AutoCAD measures from the object's corner rather than the centermark itself, producing cleaner dimension placement.
Continue building the dimensional framework. Restart the Linear Dimension tool, click on the right endpoint of the lower right centermark, then click the right endpoint of the rightmost centermark. Pull to the right and enter a distance of 1, maintaining consistent offset standards. Keep the Linear Dimension command active for efficient workflow continuation.
With the Linear Dimension tool still active, click on the top endpoint of the upper left centermark and the top endpoint of the next vertical edge to the left as illustrated. Enter a dimension line offset distance of 1 to maintain drawing consistency. This systematic approach builds a comprehensive dimensional network.
The Continue Dimension tool creates efficient chains of adjacent dimensions, essential for manufacturing drawings where cumulative tolerances matter. This tool eliminates repetitive clicking by automatically continuing from previously established dimensions.
Type DCO ENTER to start the Continue Dimension tool. By default, it continues from your last created dimension (the top left Linear Dimension). If prompted to select a dimension, click on the most recent one. Click on the next vertical edge to the right, then continue clicking the next two centermarks as shown. The tool remains active with the
<Select>option visible in the command line. Press Enter to choose this option for the next step.
Click the top extension line of the Linear Dimension on the right side between the bottom and middle centermarks as shown below. This selection tells AutoCAD which dimension chain to continue. Press Enter to choose the
<Select>option again.Now click on the right extension line of the horizontal Linear Dimension at the bottom left of the object and continue the dimension to the next centermark to the right. Press Enter twice—once to choose the select option and once to end the command. This methodical approach builds comprehensive dimension chains efficiently.
The Baseline Dimension tool offers an alternative approach to dimension chains, measuring all dimensions from a single reference point rather than point-to-point like Continue Dimension. This method proves particularly valuable when one edge serves as a critical manufacturing datum.
Type DBA ENTER to start the Baseline Dimension tool. Like the Continue tool, it defaults to using your last dimension as the baseline. The command line shows the
<Select>option—press Enter to choose it.In the front view, click on the bottom extension line of the Linear Dimension in the lower left measuring .250. Extension line selection is crucial with the Baseline tool because this specific line becomes the baseline reference for all subsequent dimensions. Pull upward and click on the next 2 vertical edges as shown below. Press ENTER twice or Esc to end the Baseline Dimension Tool. Notice how all dimensions now reference the same baseline, creating a clear manufacturing reference system.
Complete the comprehensive dimensioning by adding the two final Linear Dimensions shown below. Maintain the standard 1-inch offset distance for consistency. These final dimensions ensure that every critical measurement is clearly communicated for manufacturing and quality control purposes.
Creating Professional Centerlines
Identify Hidden Circular Features
Locate dashed lines representing hidden edges of circular holes in front views that need centerline indication.
Apply Centerline Tool
Use the Centerline command to click on pairs of dashed lines, creating centerlines that indicate circular features.
Set Proper Layer
Change to Centerlines layer before creating centerlines to maintain proper drawing organization and line standards.
Dimensions automatically update when associated objects change size or position, maintaining accuracy throughout the design process.
Editing Dimensions
Professional drawings require precise control over dimensional display and formatting. AutoCAD's dimension editing capabilities ensure your drawings meet specific industry standards and client requirements.
Dimension styles function similarly to text styles, providing consistent formatting across your entire drawing set. A style contains saved formatting options that can be applied to multiple dimensions simultaneously, ensuring uniform appearance and meeting specific drafting standards. Access these styles through the expanded Annotation Panel, the Annotate tab in the Ribbon, the Style or Dimension Toolbar, or the Properties Palette. The right-click menu provides the most efficient access during active editing.
Select the Linear Dimension below the top view measuring 1.500 and right-click. From the context menu, select the Style submenu, then choose 2 Places. Watch as the dimension updates from 3 decimal places to 2, displaying as 1.50. This style change reflects the precision requirements defined in the 2 Places Style, demonstrating how styles maintain drawing standards efficiently.
Individual precision adjustments allow fine-tuning of specific dimensions without affecting the overall style. Select the Linear Dimension at the bottom of the front view measuring 3.490. This dimension currently uses the 3 places dimension style (0.000 precision). With the dimension selected, right-click and navigate to the precision submenu, then select 4 decimal places (0.0000). The dimension now displays 3.4899, providing enhanced precision where manufacturing tolerances demand it.
Dimension text positioning affects drawing clarity and readability. Select the vertical Linear Dimension near the center of the top view measuring 6.25. Notice the text's proximity to the centerline connecting the circles creates potential confusion. Click on the text grip and drag it downward along the dimension line as shown below. This manual positioning capability ensures optimal text placement even in congested drawing areas.
Manufacturing drawings often feature repeated elements requiring quantity notation. The top view contains 5 pairs of circles, but you've dimensioned only one pair. Professional practice requires indicating that these dimensions apply to all similar features through quantity notation.
Select the Diameter Dimension in the upper left corner of the top view and double-click on the text to enter editing mode. The Text Editor Ribbon tab appears, and the dimension measurement displays with a blue background and blinking cursor. Use the right arrow key to position the cursor after the measurement text. Type x5, being careful not to overwrite the existing measurement. Press Esc to exit the Text Editor, then press Enter to accept changes. Repeat this process for the Radius Dimension at the bottom left corner. This notation clearly communicates that five instances of each circular feature exist.
Overlapping dimension lines create visual confusion and can be mistaken for object geometry in final plots. This common issue occurs in complex drawings where multiple dimensions occupy limited space. The Dimension Break tool resolves these conflicts by creating visual breaks that clearly separate overlapping elements.
In the upper right corner of the top view, observe where Extension Lines and the horizontal and vertical Linear Dimensions measuring 7.50 and 8.50 overlap. Type DIMBREAK ENTER or press the corresponding button to start the Dimension Break tool. This tool systematically creates visual breaks that eliminate confusion between dimension elements and drawing geometry, ensuring professional presentation standards.
Baseline vs Continue Dimensioning
| Feature | Baseline (DBA) | Continue (DCO) |
|---|---|---|
| Reference Point | Single baseline reference | Point-to-point chaining |
| Measurement Method | All from one origin | Cumulative segments |
| Best Use Case | Manufacturing tolerances | Sequential measurements |
Professional Dimension Editing
Style Assignment
Change dimension styles through right-click menu to control decimal places and formatting consistency.
Text Positioning
Use grips to reposition dimension text along dimension lines when clearance issues occur.
Break Overlapping Lines
Apply DIMBREAK command to create gaps in dimension lines where they intersect other drawing elements.
Key Takeaways