How to Scale in AutoCAD: Factor, Reference, Units

Short answer: type SC (SCALE), select the objects, press Enter, pick a base point (the point that stays put), then type a scale factor: 2 doubles, 0.5 halves. To make a length exactly right, type R (Reference) instead of a factor, pick the two ends of the wrong length, and type the length it should be. To convert millimetres to inches, the factor is 1/25.4.

The steps are the same in the free CADCraft app, which copies AutoCAD's command line. Everything below was run there (cadcraft-cli 0.13.0) and matches AutoCAD's behaviour unless a note says otherwise.

cadcraft.org is an independent guide, not affiliated with Autodesk. CADCraft is made by the ArtCraft team: see getartcraft.com/apps/cadcraft.

Scale by a factor

Command: SC
Select objects: (pick the objects) ↵
Specify base point: (pick a point)
Specify scale factor or [Copy/Reference] <1.0000>: 2

• Base point. Everything grows away from, or shrinks toward, this point. Pick a corner or a centre with an object snap, or type 0,0 to scale the whole drawing about the origin.
• Factor. Above 1 enlarges, below 1 shrinks, and it must be positive. Fractions work: 1/4, 1/25.4. You can also drag and click; the factor is then the distance from the base point.
• Copy. Type C before the factor to keep the original and scale a copy.
• The default in <> is the last factor you used, so Enter repeats it.

Scale to a known length (Reference)

This is the option that saves the most time: a part was drawn 37.5 long and should be 50, or an imported plan has no units and you know one wall is 4,200 mm.

Command: SC
Select objects: ALL ↵ ↵
Specify base point: (pick the left end of the edge)
Specify scale factor or [Copy/Reference] <1.0000>: R
Specify reference length <1>: (pick the left end again) (pick the right end)
Specify new length: 50

Picking the base point again as the first reference point is the trick: the edge then keeps its left end where it was. You can also type the reference length (37.5) instead of picking it.

Our test in CADCraft: the rectangle went from 37.5 × 20 to 50 × 26.6667 and the circle's radius from 4 to 5.3333. SCALE is uniform, so the height grew too. The dimension now reads 50, but its text and arrows are the same size.

CADCraft difference: at "Specify new length", AutoCAD also offers [Points] to pick the new length as two points anywhere. CADCraft 0.13.0 takes a typed length or one point measured from the base point, but not Points.

Convert units: mm, inches, metres, feet

When a drawing arrives in the wrong units, scale everything about 0,0:

Command: SC
Select objects: ALL ↵ ↵
Specify base point: 0,0
Specify scale factor or [Copy/Reference] <1.0000>: 1/25.4

In our test the 37.5 mm edge became 1.4764, which is 37.5 ÷ 25.4. Then run UNITS and set the insertion units to the new unit, so blocks and drawings you insert later come in at the right size.

How do I know which units a drawing is in? Measure something you know (a door is about 900 mm or 36 in wide) with DIST. 900 means millimetres, 0.9 metres, 36 inches.

What scales, and what doesn't

The dimension row surprises people. If the numbers are right but the text is now tiny or huge compared with the drawing, that's an annotation problem: change DIMSCALE in the dimension style (D), or the annotation scale, rather than scaling the dimensions.

Don't scale your drawing to fit the paper

The most common scaling mistake isn't a wrong factor. It's using SCALE at all to make a drawing fit a sheet.

Draw at 1:1 in real units (a 4.2 m wall is 4200 long in a millimetre drawing). Then:

• To print at 1:50, make a layout, add a viewport, and set the viewport scale to 1:50. In AutoCAD and CADCraft the status bar shows the viewport scale list when a viewport is active. In CADCraft's command line you can also run viewport.set {"scale":"1:50"} on a selected viewport, or ZOOM with 1/50XP inside it.
• To make text and dimensions read right at that scale, set the annotation scale or DIMSCALE, not the geometry.
• To print model space directly, pick the scale in the Plot dialog. DWG to PDF without losing lineweights walks through it.

If you scale the geometry down to fit, every dimension will report the wrong value and anyone who measures your file gets wrong numbers.

Other ways to resize

• ALIGN (AL) moves, rotates and, if you answer Yes to "Scale objects based on alignment points?", scales in one go: useful for fitting a traced plan onto a survey.
• STRETCH (S) changes one direction: select with a crossing window and move the corners you caught.
• Block references can have different X and Y scales (Properties palette, or INSERT with a scale per axis) when you really need non-uniform scaling.
• Grips: select objects, click a grip, then press Space to cycle to Scale. Handy for quick visual changes.

Troubleshooting

"Requires a positive number." The factor was zero, negative or not a number. Fractions like 1/2 are fine.

Things moved far away. The base point was far from the objects. Undo (U) and pick a base point on the objects.

Nothing changed size. You probably pressed Enter at the factor prompt with the default <1.0000>.

Linetypes look different after scaling. Dashes are set by LTSCALE and the object's linetype scale, which SCALE doesn't change. Adjust them separately.

Hatch disappeared or looks solid after scaling down a lot. The pattern is now very dense. Edit the hatch and raise its pattern scale.

FAQ

Related

• AutoCAD commands cheat sheet: SCALE and the other modify commands
• AutoCAD shortcuts
• DWG to PDF without losing lineweights: plot scale and paper