How-to guide · how to set units to millimeters in autocad

How to set units to millimetres in AutoCAD

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By Sumana Kumar · Published 30 May 2024 · Updated 30 May 2024

Millimetres are the working unit for most architectural and mechanical drafting outside the US, and the blocks on this site are all drawn full size in millimetres. Setting AutoCAD up properly for millimetres means more than picking 'mm' in a menu — it means getting the insertion scale, the template and the dimension settings all agreed, so blocks insert at true size and dimensions read correctly. This guide walks the complete millimetre setup, from the quickest INSUNITS toggle to a proper metric template.

The single most important setting is the insertion scale, because that is what makes downloaded blocks land at the right size. Once that is right, everything else — display precision, dimension style, the template you start from — falls into place around it. We will start with the fast fix for the current drawing, then build the durable setup so every new drawing is in millimetres without you thinking about it.

The fast way — set INSUNITS to 4

If you just need the current drawing working in millimetres right now, set one variable. Type INSUNITS, press Enter, type 4, and press Enter again. The value 4 is the code for millimetres, and it tells AutoCAD that one drawing unit equals one millimetre for the purpose of scaling inserted blocks.

With INSUNITS at 4, any millimetre block you insert lands at true size, and a metric block from a different unit (a centimetre block, say) converts correctly. This is the change that fixes 'my block came in 1000 times too big' for a metre-set drawing, or makes the blocks here behave in a fresh file. It is the fastest possible millimetre setup, though for new drawings you will want to bake it into a template, covered below.

Set it through the UNITS dialog

For a fuller, friendlier setup, use the Drawing Units dialog. Type UNITS (or UN) and press Enter.

Under 'Length', set Type to Decimal — the right choice for metric work — and pick a precision (0 or 0.0 is usually plenty for millimetre architecture; you rarely need fractions of a millimetre on screen). Then, in the 'Insertion scale' panel, set 'Units to scale inserted content' to Millimeters. That drop-down writes INSUNITS=4 behind the scenes, so it is the same setting reached through a dialog. Click OK. You now have a millimetre drawing with decimal display and correct block scaling. The dialog route is the one to teach a beginner because it shows the display and insertion settings side by side.

Start from the metric template (acadiso)

The cleanest way to work in millimetres is to start every drawing from a metric template, so the units are right before you draw anything.

When you create a new drawing (NEW), AutoCAD offers a template list. Choose acadiso.dwt (or acadiso3D.dwt for 3D) — the ISO metric template, which is pre-configured for millimetres with sensible metric defaults, as opposed to acad.dwt, which is the imperial (inch) template. Starting from acadiso means INSUNITS, dimension styles and text heights are already metric, and the blocks here drop in at true size from the first insertion. If you always work metric, set acadiso.dwt as your default template in Options > Files > Template Settings so new drawings start in millimetres automatically.

Match the dimension style to millimetres

Units and dimensions are separate settings, and a millimetre drawing needs its dimension style set to match or the numbers on the sheet will read wrong.

Open the Dimension Style Manager (DIMSTYLE or the ribbon), edit your style, and on the 'Primary Units' tab set the unit format to Decimal and a precision that suits millimetres (typically 0 — whole millimetres). Check the 'Measurement scale' factor is 1 so a 900 mm door dimensions as 900, not 0.9 or 900000. If you started from acadiso this is largely set for you, which is another reason to begin from the metric template. Getting the dimension style right is what makes the millimetre setup show up correctly on the printed drawing, not just on screen.

Save a millimetre template so it sticks

Setting millimetres in one drawing does not carry to the next; new files inherit from whatever template they start from. So the durable move is to build your own millimetre template.

Start from acadiso.dwt or a fresh file with INSUNITS=4, add your standard layers, text styles, dimension style and title block, then SAVEAS and choose 'AutoCAD Drawing Template (*.dwt)'. Give it a clear name like 'Company-mm.dwt'. From then on, start new work from that template and every drawing is in millimetres with your standards loaded. For a team, share that one template so everyone draws in the same millimetre setup — the surest way to keep block scaling and dimensions consistent across a whole project.

Check the millimetre setup worked

Before you rely on the setup, confirm it with a quick measurement, because a wrong unit is far cheaper to catch now than three sheets in.

Insert one of the millimetre blocks from this site — a door, say — at scale 1, then run DIST across a feature whose real size you know. A standard 900 mm door leaf should measure 900. If it reads 0.9, your insertion scale thinks it is metres; if it reads 900000, something is set to microns or the block is being misread. Either way, return to UNITS and confirm the insertion scale is Millimeters. One measured check after setting up the drawing gives you confidence that every block and dimension from here on will be true to size.

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Questions

Frequently asked

What's the quickest way to set AutoCAD to millimetres?+

Type INSUNITS, Enter, then 4, Enter. The value 4 is millimetres, and it sets the insertion scale so blocks land at true size. For a full setup, use the UNITS dialog and set 'Units to scale inserted content' to Millimeters.

Which template starts a drawing in millimetres?+

acadiso.dwt — the ISO metric template — is pre-configured for millimetres. Choose it in the New Drawing dialog, or set it as your default in Options > Files > Template Settings so every new drawing starts metric. acad.dwt is the imperial (inch) template.

My door block dimensions as 0.9 instead of 900 — why?+

Your insertion scale or dimension measurement scale is treating the drawing as metres. Set INSUNITS to 4 (millimetres) and check the dimension style's measurement scale is 1 on the Primary Units tab, so a 900 mm leaf reads 900.

Do I need to set units to millimetres every time I open a drawing?+

No — set it once in a drawing template (.dwt). Configure INSUNITS=4, your layers and dimension style, then SAVEAS to a template and start new drawings from it. The millimetre setup is then loaded automatically every time.

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