You've been modeling for three hours. Even so, the assembly looks clean. The mates are solid. You hit "Save" and send the STEP file to the vendor Simple, but easy to overlook..
Then the email comes back: *"Your part is 25.And 4 times too small. Did you model in inches?
You modeled in millimeters. The vendor's system defaulted to inches. Nobody checked.
This happens more than anyone admits. Not because SolidWorks makes units difficult — it doesn't. But because the unit system lives in three different places, and changing one doesn't always change the others. If you've ever scratched your head wondering why your drawing shows dual dimensions but your model properties say something else, you're not alone.
Let's fix that once and for all.
What Is the Unit System in SolidWorks
SolidWorks doesn't have a single "units setting." It has layers Small thing, real impact..
At the top level, you've got document units — what the current part, assembly, or drawing uses. This controls what you see in the status bar, what dimensions display, and what gets exported in neutral formats Worth keeping that in mind..
Below that, there's template units. Every new file starts from a template. If your template is set to IPS (inch-pound-second), every new part defaults to inches. Change the template, and you change the default for every future file Worth knowing..
Then there's application-level units — the fallback SolidWorks uses when a document doesn't specify. Most people never touch this. They should That alone is useful..
And in drawings? There's a whole separate drawing units setting that can override the model. Dual dimensions? That's yet another toggle That's the part that actually makes a difference..
The short version: units aren't a setting. They're a chain. Break one link and the whole thing drifts.
Why It Matters / Why People Care
A unit mismatch doesn't just look wrong. It ships wrong And it works..
I've seen CNC programs cut parts 25.I've seen BOMs show "0.In practice, 4x undersized because the CAM software read the STEP file in inches while the model was metric. 039 in" for a 1 mm hole because the drawing template forced dual dimensions with the wrong primary. I've watched simulation results report stress in psi on a model built in MPa — and the engineer didn't catch it until the safety factor looked "too good to be true.
Units are the silent killer of downstream workflows. CAM, FEA, PDM, ERP, 3D printing slicers — they all trust what the file says. If the file lies, everything downstream inherits the lie.
And here's the thing: SolidWorks tries to help. But not every reader respects it. It embeds unit metadata in Parasolid, STEP, and SLDPRT files. Some default to their own settings. Some strip it entirely.
So the only reliable strategy? Because of that, make sure your files are unambiguous. Every time.
How to Set Units in SolidWorks
Changing Units in an Open Document
This is the one everyone knows — and the one that causes the most confusion.
With a part or assembly open, look at the bottom-right status bar. Here's the thing — see "MMGS" or "IPS"? Click it. A menu pops up with the common systems: MMGS, CGS, MKS, IPS, and "Custom Most people skip this — try not to. Worth knowing..
Pick one. On the flip side, the model updates instantly. Dimensions on screen flip. Mass properties recalculate. The status bar reflects the new system.
But — and this trips people up — this only changes this document. It doesn't update your templates. It doesn't change future files. It doesn't touch drawings that reference this model unless you rebuild them That's the part that actually makes a difference..
Also: if you have equations, global variables, or design tables driving dimensions, those values don't auto-convert. SolidWorks doesn't rewrite your math. A "10" in an equation stays "10" — but now it means 10 mm instead of 10 inches. You have to audit it.
Easier said than done, but still worth knowing.
Setting Default Units via Templates
This is where the use lives Took long enough..
Open a blank part. Set units how you want them (status bar method above). Then go File > Save As, change "Save as type" to Part Template (.prtdot). But name it something clear: "MMGS_Standard. Practically speaking, prtdot" or "IPS_SheetMetal. Here's the thing — prtdot. " Save it to your template folder — ideally a network location your whole team uses.
Repeat for assemblies (.asmdot) and drawings (.drwdot).
Now go Tools > Options > System Options > File Locations > Document Templates. On the flip side, add that folder. Move it to the top.
Next time someone hits File > New, your template appears first. They get the right units. Practically speaking, they pick it. No status bar clicking required Small thing, real impact..
Pro tip: bake more than units into templates. Custom properties, material, annotation styles, sheet formats — all of it. A template isn't a unit setting. It's a standard.
Application-Level Default Units
Buried in Tools > Options > System Options > General, there's a "Default units" dropdown. Most people leave it at "IPS" (the install default) and forget it exists.
Here's why it matters: if you open a file that has no unit metadata — some imported STEP, a corrupted SLDPRT, a file from a system that stripped it — SolidWorks falls back to this setting. In real terms, no warning. If it's wrong, your imported geometry gets interpreted wrong. No prompt.
Set it to your shop standard. Even so, mMGS for metric shops. In practice, iPS for imperial. Done Not complicated — just consistent..
Drawing Units — The Separate Beast
Drawings have their own unit logic. Right-click the sheet > Properties. Open a drawing. There's a "Units" section with "Use document units" (the model's units) and "Override units.
If you override, the drawing displays in that system — but the model stays untouched. Dimensions show the converted values. Dual dimensions can show both.
We're talking about powerful. It's also dangerous.
Say your model is metric. You override the drawing to IPS for a US vendor. You add dual dimensions: primary inches, secondary mm. The vendor sees inches. Your shop sees mm. Everyone's happy — until someone edits a dimension in the drawing.
Editing a dimension in a drawing with overridden units writes the value back to the model in the drawing's units. You type "1.Still, 0 mm. On the flip side, the model just shrank 25. That's why 4 mm hole? Practically speaking, 0 inch. That 25.Even so, 0" in the drawing. The model now stores 1.Not 1.4x Turns out it matters..
And yeah — that's actually more nuanced than it sounds.
Never edit model dimensions from a drawing with overridden units. Add a note. Call out the conversion. But don't type in the dimension box Not complicated — just consistent..
Dual Dimensions and Alternate Unit Display
Drawings can show two unit systems simultaneously. In practice, pick primary and secondary. Which means turn it on. Tools > Options > Document Properties > Dimensions > Dual Dimensions. Set formatting — precision, trailing zeros, brackets, whatever your standard demands.
This is great for drawings that go to mixed audiences. Worth adding: it doesn't export to STEP. It doesn't affect the model. But it's a drawing-only setting. It's purely visual.
Use it intentionally. Which means document it in your drawing standard. Don't let it become a surprise.
Units in Equations, Design Tables, and Global Variables
This is the silent trap That's the part that actually makes a difference..
Equations store numbers, not unit-qualified values. Even so, if you switch the document from MMGS to IPS, that equation now drives 50 inches. And "D1@Sketch1 = 50" means 50 current document units. The sketch explodes.
Design tables (Excel-driven) are worse. The spreadsheet has no unit awareness. You type "10" in a cell
Equations and global variables are another layer where the document’s unit context can silently corrupt a design. An equation such as
WallThickness = 0.5 * Length
stores only the numeric factor 0.5. The actual thickness that SolidWorks applies is 0.On top of that, 5 × the current document unit. If the part file is opened in a metric environment, the same equation now yields a thickness of 0.5 mm instead of 0.5 in, and the sketch may become under‑defined or over‑defined in ways that are not obvious from the equation itself Nothing fancy..
Design tables operate on the same principle. A spreadsheet row that reads
PartLength, 12.0
does not carry any unit qualifier. And when the part file is saved with a different unit system, the value 12. Because of that, 0 is interpreted in the new system, potentially inflating or shrinking every feature that references that table entry. In practice, the safest approach is to keep a dedicated “unit” column in the table or to embed the unit directly in the cell (e. Think about it: g. , “12 in”) and then use a custom property or a separate conversion factor in the model to translate that value into the document’s native units Most people skip this — try not to..
Global variables behave similarly. A variable defined as
Diameter = 100
will always represent 100 of whatever unit the part is currently set to. If the part file is later saved as a different unit system, the diameter changes accordingly, which can break downstream assemblies that expect a fixed size. g.Which means to prevent this, many teams store the unit explicitly in the variable name (e. g., Diameter_mm) or create a separate conversion variable (e., Diameter_in = Diameter_mm / 25.4) and reference the conversion variable in all downstream equations.
Best‑Practice Checklist for Units
- Set the document units once – verify the “Default units” dropdown matches the shop’s standard before opening any files.
- Lock drawing units – keep the “Use document units” option enabled unless a specific override is required, and never edit dimensions in a drawing that has an overridden unit setting.
- Document dual‑dimension intent – if a drawing must show both metric and imperial, note the primary system in the drawing title block and include a conversion note near any critical dimensions.
- Treat equations and tables as unit‑agnostic – always multiply or divide by a known conversion factor to translate between systems, and store the conversion factor as a separate global variable for easy updates.
- Audit imported files – after importing STEP, IGES, or other neutral formats, open the part’s property manager and confirm the units displayed match expectations; if not, re‑import with the correct unit setting or apply a manual scale correction.
Conclusion
Units are the invisible foundation of every SolidWorks model, drawing, equation, and table. A mismatched unit setting can silently reshape geometry, corrupt design intent, and generate costly rework that could have been avoided with a simple checklist. Also, by establishing a clear unit standard, confirming it on every file open, respecting the separation between model and drawing units, and explicitly handling conversions in equations, design tables, and global variables, engineers eliminate the most common source of hidden errors. When units are managed deliberately, the full power of SolidWorks—precise modeling, accurate documentation, and seamless collaboration—can be realized without surprise.
