How to set INSUNITS in AutoCAD

What INSUNITS actually controls

INSUNITS sets the drawing's insertion scale unit — the real-world meaning of one drawing unit for the purpose of scaling inserted content. It pairs with each block's own stored unit.

When you insert a block, AutoCAD looks at the block's unit and at your drawing's INSUNITS, works out the ratio, and scales the block by that ratio automatically. A millimetre block (block unit = mm) inserted into a metre drawing (INSUNITS = Meters) is scaled by 0.001, so a 1700 mm bath becomes 1.7. The same block in a millimetre drawing (INSUNITS = Millimeters) is scaled by 1 and stays 1700.

Crucially, INSUNITS does nothing to geometry you draw by hand and nothing to blocks already placed. It only governs the scaling applied at the moment of insertion.

The INSUNITS value codes

INSUNITS accepts an integer that names the unit. The ones you will actually use are near the top of the list, but the full common set is worth knowing.

- 0 = Unitless (no conversion — avoid for block work) - 1 = Inches - 2 = Feet - 3 = Miles - 4 = Millimeters - 5 = Centimeters - 6 = Meters - 7 = Kilometers

The list continues into microinches, mils, yards and astronomical units, but those rarely come up in building or product drafting. For the millimetre blocks on this site, the value you want for a millimetre drawing is 4. For a metre-based drawing, use 6. For a US architectural template, 1 (inches) or 2 (feet) matches the template and still converts the metric block correctly.

Setting INSUNITS on the command line

The fastest route is to set the variable directly. Type INSUNITS and press Enter; AutoCAD shows the current value and prompts for a new one. Type the code — 4 for millimetres — and press Enter. That is the whole operation.

Because it is a system variable, you can also set it inside a script or a tool macro, which is handy if you maintain office standards. A one-line macro that sets INSUNITS to 4 at the start of a routine guarantees blocks scale correctly no matter which template a colleague started from. Setting it on the command line changes the current drawing only; to make it stick for new drawings, set it and then save the file as your template, covered below.

Setting INSUNITS through the UNITS dialog

If you prefer a dialog, the same setting lives in the Drawing Units window. Type UNITS (or UN) and press Enter.

In the dialog, find the 'Insertion scale' panel and the drop-down 'Units to scale inserted content'. Choosing an entry here writes the matching INSUNITS value behind the scenes — pick Millimeters and INSUNITS becomes 4. The dialog is the friendlier route when you are not sure of the numeric codes, and it sits right next to the linear-unit format controls, so you can set display precision at the same time. Click OK to apply. Whichever route you use, dialog or command line, the result is identical because both write the same system variable.

INSUNITSDEFSOURCE and INSUNITSDEFTARGET

Two companion variables handle the awkward case of blocks that don't declare their own units.

INSUNITSDEFSOURCE sets the unit AutoCAD assumes for a source block whose own unit is Unitless. Set it to 4 (millimetres) and any unitless metric block is treated as millimetres on insertion, so it converts sensibly instead of arriving raw.

INSUNITSDEFTARGET sets the assumed unit of the current drawing when its own INSUNITS is Unitless — a fallback for the receiving side. In a tidy setup where every drawing has a real INSUNITS, this rarely fires, but pointing it at millimetres too keeps behaviour predictable. The blocks on this site carry their units, so these defaults mainly rescue older, unitless files you have collected, but setting both to 4 is good hygiene.

Make INSUNITS permanent in your template

Setting INSUNITS in one drawing fixes that drawing only; every new file resets to the template's value. So the durable fix is to set it in the template itself.

Start a fresh drawing, set INSUNITS to your standard (4 for millimetre work), set INSUNITSDEFSOURCE to 4 as well, add your layers and styles, then SAVEAS and choose 'AutoCAD Drawing Template (*.dwt)'. Start all new work from that .dwt and INSUNITS is correct before you draw a single line.

For a team, distributing one standard template means every drafter inserts blocks against the same unit assumption. That is the quiet, structural fix for wrong-size blocks across a whole office — not policing scale factors by hand, but making the variable right by default so the conversion always just works.