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Understanding line weights

A guide to what heavy, medium, and light lines represent in construction documentation. Line weight hierarchy creates visual depth and helps readers understand what they're looking at.

The core principle

"What you cut through is heaviest. What you see beyond is lighter."

This hierarchy creates depth perception in 2D drawings, helping viewers understand spatial relationships.

Line weight visual comparison
Extra Heavy
0.70-1.00mm
Heavy
0.50-0.60mm
Medium
0.35-0.40mm
Light
0.25mm
Extra Light
0.13-0.18mm

Line Weight Standards

Extra Heavy
0.70-1.00 mm (0.028-0.039")

The boldest lines on a drawing. Used sparingly for maximum emphasis and boundary definition.

Property linesTitle block bordersSection cut poché
Heavy
0.50-0.60 mm (0.020-0.024")

Shows elements that are cut through in plan or section. The primary hierarchy line that defines what you're cutting through.

Cut lines (section cuts)Object outlines at cut planeMain building outlinesGrade lines
Medium
0.35-0.40 mm (0.014-0.016")

Shows elements visible but not cut. Objects in elevation or beyond the cut plane in plans and sections.

Object lines beyond cutElevation outlinesMajor equipmentVisible edges
Light
0.25 mm (0.010")

Secondary information that supports the drawing but shouldn't dominate visually.

Dimension linesLeader linesHatch patternsWindow mullionsMinor details
Extra Light
0.13-0.18 mm (0.005-0.007")

Reference information and background context. Should be visible but recede visually.

Construction linesCenterlinesGrid linesHidden linesBackground elements

Line Types (Patterns)

Continuous
Visible edges, object outlines, cut lines
Dashed (Hidden)
Hidden lines, objects above cut plane, future work
Centerline
Axes of symmetry, column grids, centerlines
Property/Boundary
Property lines, easements, setbacks
Dotted
Property above, demolition, or alternate positions
Break Line
Shortened views of continuous elements

Application by Drawing Type

Floor Plans
Walls cut at 4' (Heavy)
Casework, fixtures (Medium)
Dimensions, hatching (Light)
Elements above cut (Dashed)
Building Sections
Structure, walls cut (Heavy)
Elements in elevation (Medium)
Background elements (Light)
Grade line (Extra Light)
Elevations
Building outline (Heavy)
Windows, doors, major features (Medium)
Material patterns, details (Light)
Details
Section cuts, main assembly (Heavy)
Component outlines (Medium)
Fasteners, annotations (Light)

Based on standard architectural drafting conventions and AIA CAD Layer Guidelines. Individual firms may use variations. Always check project-specific standards.

Keep exploring

More drafting and drawing review references.

Drawing Types Explained

Plans, sections, elevations, and details, what each drawing type shows.

Architectural Plan Symbols

Visual reference for symbols used on architectural drawings.

Sheet Organization Guide

How construction drawing sets are numbered and organized.

AI Plan Review Guide

How AI tools interpret and analyze construction drawings.

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