Offset: parallel copies at a distance
OFFSET creates a parallel copy of a line, arc, circle or polyline at a set distance. It’s how drafters turn a single line into a wall, a kerb or a boundary setback.
In this lesson you will
- Offset objects by a set distance
- Use the Through, Erase and Layer options
- Offset polylines to create walls
- Combine offset with trim and fillet
How OFFSET works
AutoCAD remembers the last distance, so repeating offsets is quick. Offsetting a circle or arc gives a concentric copy; offsetting a closed polyline gives a larger or smaller outline in one step.
- 1Type
Oand Enter. - 2Type the offset distance, e.g.
230, and Enter. - 3Pick the object to offset.
- 4Click on the side where the copy should go.
- 5Pick another object or press Enter to finish.
Useful options
| Option | What it does |
|---|---|
Through (T) | Offsets through a point you pick instead of a distance |
Erase (E) | Deletes the original after offsetting |
Layer (L) | Puts the copy on the current layer instead of the source layer |
Multiple (M) | Keeps offsetting the new copy repeatedly |
Drawing walls with offset
A common workflow: draw the internal face of the external walls as one closed polyline, then offset it outward by the wall thickness (e.g. 230 for brick, 90 or 110 for internal studs plus lining). Internal walls: draw a centreline, offset it half the wall thickness each side, erase the centreline and trim the junctions.
Because polylines offset as one piece, corners stay clean automatically.
Set the current layer to your wall layer and use OFFSET's Layer › Current option, so the new wall face lands on the right layer.
Cleaning up after offset
Where walls meet, use TRIM to remove overlaps and FILLET with radius 0 to close corners. The Practical projects use this sequence repeatedly.
Quick reference
| Command / tool | How to start it | What it does |
|---|---|---|
| OFFSET | O | Parallel copy at a distance |
| OFFSETGAPTYPE | System variable | How polyline corners are filled when offsetting outward (0 = extend, 1 = arc) |
Common mistakes
Offset produces lots of small separate lines.
Join the original into a polyline first (JOIN).
Offset goes the wrong way.
Click clearly on the side you want; zoom in if two sides are close.
Exercise
External and internal walls
- Draw a 9000 × 7000 closed polyline (internal face of external walls).
- Offset it 230 outward.
- Draw a vertical centreline for an internal wall at 5000 from the left, between the internal faces.
- Offset the centreline 45 each side (a 90 wall), then erase the centreline.
- Trim the junctions cleanly.
You should end up with: A shell with a clean internal wall — the start of a floor plan.
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Lesson quiz
You offset a closed polyline outward by 230. What do you get?
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