What is Line Weight in Drawing?

Line weight (also called line thickness) is the thickness or width of a line used in a technical drawing. Different line weights help distinguish between various features, making drawings easier to read and interpret.

In engineering drawings, thick and thin lines are used according to standards such as ISO 128 and ASME Y14.2.

Why is Line Weight Important?

Line weight helps to:

Improve the readability of drawings.
Differentiate between visible and hidden features.
Emphasize important parts of a drawing.
Communicate design intent clearly.
Meet engineering drawing standards.

Types of Line Weights

1. Thick Lines

Used for important or prominent features.

Applications:

Visible object outlines
Cutting plane lines
Border lines

Example:
The outer edges of a machine component are drawn with thick lines.

2. Thin Lines

Used for secondary information.

Applications:

Dimension lines
Extension lines
Hidden lines
Center lines
Section (hatching) lines
Leader lines

Example:
The dimension indicating a hole diameter is drawn with thin lines.

Common Line Weight Values

Modern CAD software allows you to select standard line weights. Common values include:

Line Weight (mm)	Typical Use
0.13	Very fine details
0.18	Small text and fine lines
0.25	Dimension and extension lines
0.35	Hidden and center lines
0.50	Visible object lines
0.70	Cutting planes and borders
1.00	Large borders or emphasis

The exact values used may vary depending on company standards and drawing scale.

Typical Line Weight Applications

Line Type	Typical Weight
Visible (Object) Line	Thick (0.5–0.7 mm)
Hidden Line	Thin (0.25–0.35 mm)
Center Line	Thin (0.25–0.35 mm)
Dimension Line	Thin (0.25 mm)
Extension Line	Thin (0.25 mm)
Section (Hatching) Line	Thin (0.25 mm)
Cutting Plane Line	Thick (0.7 mm)

Example

Imagine a drawing of a rectangular block with a hole:

The outer edges of the block are drawn with thick object lines.
The hidden edges of the hole are shown with thin dashed lines.
The centerline of the hole is a thin chain line.
The dimensions (e.g., 100 mm length, Ø20 mm hole) are indicated with thin dimension and extension lines.

This variation in line weight makes it easy to distinguish between different types of information.

Line Weight in CAD Software

Most CAD programs (such as AutoCAD, SolidWorks, and DraftSight) allow you to assign line weights to:

Layers
Individual objects
Plot styles

For example:

Object layer: 0.50 mm
Dimension layer: 0.25 mm
Centerline layer: 0.25 mm
Hidden layer: 0.35 mm

Benefits of Proper Line Weight

Enhances drawing clarity.
Improves visual hierarchy.
Makes drawings easier to interpret.
Reduces errors during manufacturing.
Ensures compliance with engineering standards.

Summary

Line weight is the thickness of a line in a technical drawing. Different line weights are used to distinguish visible outlines, hidden features, dimensions, centerlines, and cutting planes.