Linear dimension in AutoCAD - Step-by-Step Guide

Introduction

Linear dimension in AutoCAD helps you measure and show the exact length between two points in your drawing. It solves the problem of needing clear, precise measurements for parts or spaces in your design.

When you want to show the length of a wall in a building plan.

When you need to measure the distance between two holes on a mechanical part.

When you want to display the width of a window in an architectural drawing.

When you need to check the size of a component before manufacturing.

When you want to add clear size details to a technical drawing for others to understand.

Steps

Step 1: Click

- Annotate tab on the ribbon

The annotation tools panel opens showing dimension options

Step 2: Select

- Linear dimension tool in the Dimensions panel

The command line prompts you to specify the first extension line origin

Step 3: Click

- First point on the object or drawing area

The command line prompts you to specify the second extension line origin

Step 4: Click

- Second point on the object or drawing area

The dimension line appears showing the distance between the two points

Step 5: Move

- Cursor to position the dimension line

The dimension line is placed where you click, showing the measurement clearly

Before vs After

Before

Drawing shows two points with no measurement between them

After

A linear dimension line appears between the two points showing the exact distance, for example, 1500 mm

Settings Reference

Dimension style

📍 Annotate tab > Dimension Style panel > Dimension Style Manager

Controls the appearance of dimensions including text size, arrow style, and units

Default: Standard

Dimension units

📍 Dimension Style Manager > Modify > Primary Units tab

Sets the unit format for the dimension measurement

Default: Decimal

Text height

📍 Dimension Style Manager > Modify > Text tab

Controls the size of the dimension text for readability

Default: 2.5 (units depend on drawing scale)

Common Mistakes

Clicking points that are not aligned horizontally or vertically

Linear dimension measures straight horizontal or vertical distances only, so misaligned points give incorrect or skewed results

Ensure the two points are aligned horizontally or vertically before applying the linear dimension

Using the wrong dimension style causing text or arrows to be too small or large

Dimension styles control readability and clarity; wrong styles make the drawing hard to understand

Set or modify the dimension style to match your drawing scale and standards before placing dimensions

Summary

Linear dimension measures and displays the straight distance between two points in AutoCAD.

Use it when you need clear size details in your drawings for construction or manufacturing.

Make sure points are aligned and dimension styles are set correctly for accurate and readable measurements.

Practice

1. What does a linear dimension in AutoCAD represent?
DIMLINEAR is used to create it.

easy

A. The straight distance between two points

B. The angle between two lines

C. The radius of a circle

D. The area of a shape

Solution

1. Step 1: Understand the purpose of linear dimension

   Linear dimension measures the straight distance between two points in a drawing.

2. Step 2: Recognize the command used

   DIMLINEAR is the AutoCAD command to create linear dimensions.

3. Final Answer:

   The straight distance between two points -> Option A

4. Quick Check:

   Linear dimension = straight distance [OK]

Hint: Linear dimension always measures straight distance [OK]

Common Mistakes:

• Confusing linear dimension with angular dimension
• Thinking it measures radius or area
• Mixing up commands like DIMANGULAR

2. Which of the following is the correct command to create a linear dimension in AutoCAD?

easy

A. DIMANGULAR

B. DIMDIAMETER

C. DIMRADIUS

D. DIMLINEAR

Solution

1. Step 1: Recall AutoCAD dimension commands

   DIMLINEAR is used for linear dimensions, DIMANGULAR for angles, DIMRADIUS for circle radius, and DIMDIAMETER for circle diameter.

2. Step 2: Match command to linear dimension

   Since linear dimension measures straight distance, the correct command is DIMLINEAR.

3. Final Answer:

   DIMLINEAR -> Option D

4. Quick Check:

   Linear dimension command = DIMLINEAR [OK]

Hint: DIMLINEAR command creates straight distance dimensions [OK]

Common Mistakes:

• Choosing DIMANGULAR which measures angles
• Confusing radius and diameter commands
• Typing commands with typos

3. Given two points at coordinates (2,3) and (8,7), what will the linear dimension show as the distance?

medium

A. 10 units

B. 7 units

C. 6.4 units

D. 5 units

Solution

1. Step 1: Calculate the distance between points (2,3) and (8,7)

   Use the distance formula: sqrt((8-2)^2 + (7-3)^2) = sqrt(6^2 + 4^2) = sqrt(36 + 16) = sqrt(52) ≈ 7.211.

2. Step 2: Check options for closest value

   Compare to ≈7.211: 7 units (closest, diff ≈0.211), 10 units (too high), 6.4 units (diff ≈0.811), 5 units (too low).

3. Step 3: Recalculate carefully

   sqrt(52) ≈ 7.211, so 7 units is closest to actual distance.

4. Final Answer:

   7 units -> Option B

5. Quick Check:

   Distance formula = 7 units [OK]

Hint: Use distance formula sqrt((x2-x1)^2+(y2-y1)^2) [OK]

Common Mistakes:

• Using wrong coordinates order
• Forgetting to square differences
• Choosing approximate values without calculation

4. You used DIMLINEAR but the dimension line is not showing the correct distance. What could be the issue?

medium

A. You selected points that are not aligned horizontally or vertically

B. You used the wrong command; should use DIMANGULAR

C. You forgot to set the scale factor

D. You did not select the dimension style

Solution

1. Step 1: Understand DIMLINEAR behavior

   DIMLINEAR measures horizontal or vertical distance between points. If points are diagonal, it may not show expected distance.

2. Step 2: Identify common mistake

   If points are not aligned horizontally or vertically, the dimension line may appear incorrect or skewed.

3. Final Answer:

   You selected points that are not aligned horizontally or vertically -> Option A

4. Quick Check:

   DIMLINEAR needs horizontal/vertical points [OK]

Hint: DIMLINEAR works best with horizontal or vertical points [OK]

Common Mistakes:

• Using DIMANGULAR instead of DIMLINEAR
• Ignoring scale factor settings
• Not applying dimension style

5. You want to dimension a slanted line between points (1,1) and (4,5) using DIMLINEAR. How do you ensure the dimension line shows the true length of the line?

hard

A. Use DIMLINEAR only between points aligned horizontally

B. Use DIMANGULAR to measure the angle instead

C. Use DIMLINEAR with the rotated option aligned to the line angle

D. Use DIMRADIUS to measure the length

Solution

1. Step 1: Understand limitation of DIMLINEAR

   DIMLINEAR measures horizontal or vertical distances by default, so for slanted lines, it needs rotation.

2. Step 2: Use rotated dimension option

   DIMLINEAR has a rotated option to align the dimension line along the angle of the slanted line, showing true length.

3. Step 3: Confirm other options are incorrect

   DIMANGULAR measures angles, not length; DIMRADIUS measures circle radius; horizontal alignment only works for horizontal lines.

4. Final Answer:

   Use DIMLINEAR with the rotated option aligned to the line angle -> Option C

5. Quick Check:

   Rotated DIMLINEAR shows true length [OK]

Hint: Rotate DIMLINEAR to line angle for true length [OK]

Common Mistakes:

• Using DIMANGULAR instead of linear dimension
• Trying to dimension slanted line without rotation
• Confusing radius with length measurement