INSUNITS is the AutoCAD setting that answers a simple question: what is one unit in this drawing? AutoCAD doesn’t need to know to draw lines, but it does need to know when content moves between drawings. Blocks, xrefs, images and content dragged from DesignCenter or the Blocks palette are all scaled using INSUNITS, so a drawing with the wrong value causes trouble every time you bring something in.
Where to find it
INSUNITS is a system variable saved in each drawing. You can type INSUNITS at the command line to see or change its number, or open UNITS, where it appears under Insertion scale as “Units to scale inserted content”. Changing it doesn’t move or resize anything that is already drawn; it only changes how future inserted content is scaled.
It is independent of LUNITS, the length type. Architectural and engineering formats show feet and inches but are drawn in inches, so an architectural drawing should have INSUNITS set to inches, not feet.
The values you’ll use
| INSUNITS | Unit | Typical drawings |
|---|---|---|
| 0 | Unspecified (unitless) | Old files, files from other programs |
| 1 | Inches | US architecture, interiors, furniture |
| 2 | Feet | Some civil and site work |
| 4 | Millimeters | Metric architecture and product design |
| 5 | Centimeters | Some interior and furniture drawings |
| 6 | Meters | Metric site plans and urban design |
| 21 | US survey feet | Civil drawings on state plane coordinates |
There are more values, from miles to light years, but these are the ones that show up in building drawings.
How AutoCAD uses it when you insert a block
When you insert a drawing file as a block, AutoCAD reads INSUNITS in the source file and in the drawing you’re working in, and multiplies the block by the ratio between them. A file in inches (1) inserted into a drawing in millimeters (4) is scaled by 25.4; the same file inserted into a drawing in feet (2) is scaled by 1/12. The scale you type in the insert dialog is applied on top of that, so normally you leave it at 1.
Blocks defined inside a drawing carry their own units too: when you create a block with BLOCK, the dialog has a Block unit setting, and that is what AutoCAD compares against when the block is copied into another drawing through DesignCenter or the Blocks palette.
When one side is unitless
If either drawing has INSUNITS 0, AutoCAD can’t work out the ratio and uses two fallback settings instead, found under Options › User Preferences › Insertion scale:
INSUNITSDEFSOURCE: the units assumed for inserted content that has no units.INSUNITSDEFTARGET: the units assumed for the current drawing when it has none.
These are saved in the user’s profile, not in the drawing, which is why the same file can insert at different sizes on two computers in the same office. The reliable fix is not to depend on them: set INSUNITS in every drawing and template.
Xrefs, images and PDFs
External references (XATTACH) are scaled the same way as blocks, using the units of the referenced drawing. Raster images and PDF underlays use their own resolution or the scale you enter, combined with the drawing’s INSUNITS, so an image attached into a drawing with the wrong units comes in at the wrong size just like a block.
Setting it up properly
- Open your template (
.dwt). - Run
UNITSand set the insertion scale to the unit you draw in: inches for most US building work, millimeters for metric work. - Save the template. Every new drawing started from it will carry the right value.
- For existing drawings, set INSUNITS once in each one and save. Check a known dimension with
DISTfirst so you set the value the drawing really uses, not the one you expect.
A drawing that says it is in millimeters but was actually drawn in inches is worse than a unitless one, because blocks will be converted confidently to the wrong size.
How the files on cadgrid.net are set
Every block comes as two DWG files saved in AutoCAD 2000 format. The inch file is drawn in inches with INSUNITS 1 and the millimeter file in millimeters with INSUNITS 4, both at real size with the base point at 0,0. Insert either into a drawing that has its insertion scale set and AutoCAD converts it; insert the matching one and the conversion factor is simply 1.
Troubleshooting checklist
- Block is 25.4× too big or small: inch/millimeter mismatch. Check INSUNITS on both sides.
- Block is 12× off: one side is set to feet, the other to inches.
- Sizes differ between computers: one drawing is unitless and the two profiles have different INSUNITSDEFSOURCE or INSUNITSDEFTARGET values.
- Dimensions read correctly but blocks come in wrong: the length format is right but the insertion scale isn’t; they are separate settings.
