8.3 Offsetting Objects

OFFSET is one of the most frequently used precision-drafting commands in everyday AutoCAD work, because so much real-world geometry is naturally described as "parallel to this, a fixed distance away" — a second wall line representing thickness, a series of concentric circles, a road centerline paired with its edge lines. The ACU AutoCAD exam tests both the basic distance-based workflow and the Through-point alternative, along with the option settings that control how the new copy behaves.

The Basic Distance Workflow

Running OFFSET first prompts for an offset distance (or one of the bracketed options). Typing a number sets that value as the fixed distance for the operation. AutoCAD then asks you to select the object to offset, followed by a prompt to specify a point on the side you want the copy placed — not a precise measured point, just a rough click indicating direction. AutoCAD places the new copy parallel to the original, offset by the typed distance, on whichever side of the original object your click landed on.

The Through Option: Passing Through a Specific Point

Instead of typing a fixed distance, typing T for Through switches the workflow: after selecting the object to offset, AutoCAD asks you to specify a through point rather than a side. The resulting copy is placed parallel to the original, positioned so that it passes exactly through whatever point you pick — useful when you know a specific point the new line needs to hit (such as an existing door jamb or column centerline) but don't know or don't care about the exact numeric distance involved.

Multiple Offsets in One Pass

After the first offset copy is placed, AutoCAD continues prompting for additional side picks at the same fixed distance without requiring you to restart the command, letting you click repeatedly to stack several evenly spaced parallel copies outward from the same source object — useful for quickly generating a series of contour lines or evenly spaced parallel wall studs from one original line.

Erase and Layer Options

Two supporting options change what happens to the source object and which layer the new copy lands on:

• Erase deletes the original source object immediately after the offset copy is created, useful when the offset copy is meant to fully replace the original rather than exist alongside it.
• Layer toggles whether the new offset copy is placed on the Current (active) layer or on the Source object's own layer, letting a drafter decide whether offset copies should automatically inherit the layer of whatever they were copied from or always land on whatever layer happens to be active at the time.

Offsetting Closed Shapes: Inward vs. Outward

For a closed object — a circle, ellipse, or closed polyline such as a rectangle — the side you click determines whether the copy shrinks inward or grows outward. Clicking a point inside the shape's boundary produces a smaller, nested copy inside the original; clicking a point outside the boundary produces a larger copy surrounding the original. For a circle specifically, offsetting inward reduces the radius by the offset distance, while offsetting outward increases the radius by that same distance — a 10-foot-radius circle offset outward by 2 feet becomes a 12-foot-radius circle, while offset inward by 2 feet it becomes an 8-foot-radius circle.

A closed rectangular polyline behaves the same way at every side simultaneously: offsetting inward by a fixed distance shrinks all four sides uniformly toward the center, while offsetting outward grows all four sides uniformly outward, keeping the shape's overall proportions consistent as long as the offset distance is smaller than half the shape's narrowest dimension.

Corner Handling on Polylines with Sharp Bends

When a polyline being offset has sharp bends rather than smooth curves, the two offset segments at each corner may not meet cleanly, leaving either a small gap or an overlapping overshoot. AutoCAD resolves this using a configurable corner-fill behavior with three settings: extend the two segments to a sharp point (the default), fillet the corner with a small rounded arc, or chamfer the corner with a straight beveled cut — the same three corner treatments covered later in this chapter for FILLET and CHAMFER, applied automatically wherever OFFSET needs to close a gap at a polyline vertex.

What OFFSET Can and Cannot Be Used On

OFFSET is limited to true curve-type objects: lines, arcs, circles, ellipses and elliptical arcs, 2D polylines (open or closed), splines, rays (offsetting a ray produces another ray extending in the same single direction), and construction lines / xlines (which offset as a parallel line extending infinitely in both directions, matching the original). OFFSET rejects text, blocks, hatches, dimensions, and points outright with an error — none of these object types have the kind of continuous parallel-path geometry that OFFSET needs to generate a copy from.

Worked Example

An exterior wall is drawn as a single closed rectangular polyline, 20 feet by 15 feet, representing the outer face of the wall. Running OFFSET, typing a distance of 0.5 (6 inches), selecting the rectangle, and clicking a point inside it produces a second, smaller rectangle 19 feet by 14 feet, representing the wall's interior face — a 6-inch wall thickness on every side. If instead the drafter needed the new line to pass through a specific interior column centerline rather than a fixed 6-inch offset, typing T for Through, selecting the rectangle, and picking that column's center point would place the parallel line exactly through it instead.

On the Exam

Expect questions describing a click location relative to a closed shape and asking whether the result grows or shrinks, questions distinguishing the Through option's picked-point approach from the standard fixed-distance workflow, and questions testing which object types OFFSET can and cannot be used on directly.