Change units in SolidWorks through the Document Properties menu

Open the file you want to change, then go to File > Properties and click the Document Properties tab. Under Units, select your desired system from the dropdown — inches, millimeters, feet, or centimeters are the most common choices. Click OK to explore the change to that file.

The change affects only the file you have open. If you want all new files to start in a specific unit system, you can set a default in Tools > Options > Document Properties > Units, then save that as your template. Every sketch and part you create from that point will use your chosen units.

Changing units does not convert your existing geometry — a part drawn in inches stays the same physical size if you switch to millimeters. The numbers change, but the actual model does not. If you need to scale a part to a different size, you use the Scale feature under Insert > Features instead.

Key Takeaways

  • Units are set per file through File > Properties > Document Properties > Units, and the change applies only to that file.
  • Changing units changes the display numbers but not the physical size of your model — a 10-inch part stays the same size if you switch to millimeters and see 254 mm.
  • To make all new files start in a specific unit system, set your default in Tools > Options > Document Properties > Units and save it as your template.
  • If you need to actually resize a part to a different scale, use Insert > Features > Scale rather than changing the unit system.

Why the unit system matters for your workflow

The unit system you choose affects how you read dimensions, how you communicate with manufacturers, and whether your file plays well with other software. If you are designing parts for a shop that works in inches, switching your file to millimeters creates confusion when you send drawings. If you are importing a part from a supplier who works in metric, your file needs to match to avoid scaling errors.

SolidWorks also ties units to precision — the software assumes a certain decimal place based on your system. A file in inches typically shows three decimal places by default (0.001 inch precision), while millimeters show two (0.01 mm precision). If you need tighter tolerances, you may need to adjust the decimal display separately after changing units.

Changing units in sketches and drawings

When you change the document units, sketches update automatically to show the new numbers. A sketch dimension that read 2.5 inches will display as 63.5 millimeters if you switch to metric. The sketch itself does not change — only the labels do.

Drawings (the 2D sheets you create from your 3D model) also update when you change document units, but you may need to refresh the view. If a drawing still shows old dimensions after you change units, right-click on the drawing sheet and select Update. If you have custom dimension text or notes in your drawing, those do not convert automatically — you need to edit them by hand.

Setting up a template with your preferred units

Rather than changing units every time you start a new project, create a template file with your preferred system already set. Open a blank part file, go to File > Properties > Document Properties, set your units, then save the file as File > Save As and choose Part Template (*.prtdot) from the file type dropdown.

Give the template a clear name like "Part_Metric" or "Part_Inches" so you can find it later. When you start a new project, go to File > New, select Templates, and choose your saved template. Every new part you create from that template will start with your chosen units already in place.

You can create separate templates for different workflows — one for metric work, one for imperial, one with your company's standard layer setup, and so on. This saves time and prevents the mistake of designing an entire part in the wrong unit system.

Converting between unit systems in existing files

If you inherit a file from someone else and need to work in a different unit system, changing the document units is the first step. However, you should verify that the change makes sense for your workflow. Open the file, check what units it currently uses (look at the title bar or the Document Properties), then decide whether to convert or keep it as-is.

If the file came from a supplier or manufacturer, ask them what units they designed in before you change anything. Converting a metric file to inches and back can introduce rounding errors if you do it multiple times. It is safer to keep the file in its original units and convert only the dimensions you need to communicate to your team.

Troubleshooting unit-related problems

If your part suddenly looks much larger or smaller after changing units, you changed the display units but the geometry did not scale. This is normal behavior. To fix it, undo the unit change, then use Insert > Features > Scale to resize the part to the correct physical dimensions before changing units again.

If you are importing a part from another CAD program and it appears at the wrong scale, the problem is usually a unit mismatch. Check what units the imported file used, then set your SolidWorks document to match before importing. If you have already imported it, delete the imported feature, change your document units, and import again.

If dimensions in your drawing do not match the model after a unit change, right-click the drawing sheet and select Update. If that does not work, the drawing may have custom text or locked dimensions — check each dimension individually and update it by hand if needed.

Frequently Asked Questions

Does changing units scale my model to a different size?

No. Changing units only changes how the numbers are displayed. A 10-inch part stays the same physical size; it just shows as 254 mm. If you need to actually make the part larger or smaller, use the Scale feature under Insert > Features instead of changing units.

Can I change units for just one sketch or feature?

No, units are set at the document level and explore to the entire file. However, you can create a new file in different units, design the feature there, and then insert it into your main file. This is rarely necessary — most workflows use one unit system per project.

What happens to my drawings when I change document units?

Drawings update automatically to show the new unit numbers. If a drawing still displays old dimensions, right-click the sheet and select Update. Custom text or notes in the drawing do not convert automatically and must be edited by hand.

How do I set a default unit system so I do not have to change it every time?

Go to Tools > Options > Document Properties > Units, set your preferred system, then save a blank part as a template file (File > Save As > Part Template). When you create new files, choose that template and it will start with your preferred units already set.

What should I do if I receive a file in the wrong units?

Check the current units in File > Properties > Document Properties > Units. If you need to work in different units, change the document units there. If the file came from a supplier, ask them what units they used before making changes, as converting back and forth can introduce rounding errors.