Change units in Fusion 360 through the Preferences menu

Open Fusion 360 and go to the menu in the top left corner. Click Preferences (on Mac, this is under Fusion 360 > Preferences). In the Preferences window, select Units from the left sidebar. You will see a dropdown menu showing your current unit system — this is where you switch between metric (millimeters, centimeters) and imperial (inches, feet). Choose the unit system you need and click OK.

The change takes effect immediately for any new sketches or designs you create. If you have an existing design open, Fusion 360 will convert all your measurements to the new unit system automatically. A design that was 100 millimeters wide becomes 3.94 inches wide when you switch to imperial — the actual size stays the same, only the numbers change.

You can also change units for a single document without changing your overall preferences. Open the document, go to File > Properties, and look for the Units field. This method is useful when you are working on a project that needs different units than your default setting.

Key Takeaways

  • Units are changed through Preferences > Units in the top menu, and the change applies to all new work immediately.
  • Switching units converts all existing measurements in your current design, but the physical size of your model stays the same.
  • You can change units for a single document through File > Properties without affecting your default preference setting.
  • Fusion 360 supports metric units (millimeters, centimeters) and imperial units (inches, feet) in the same project.
  • If you work with a team, confirm which unit system the project uses before you start, because switching mid-project can cause confusion.

Why your measurements show the wrong numbers after switching

When you change units, Fusion 360 converts the numbers but keeps the geometry the same size. If you created a part that is 10 inches wide and switch to millimeters, that part is now 254 millimeters wide — it did not grow or shrink, the measurement just changed. This is the correct behavior for most work, but it can be confusing if you expect the numbers to stay the same.

The confusion usually happens when someone switches units, sees different numbers, and thinks the model changed size. It did not. Open the model in the original unit system and measure it — you will see the same physical dimensions. The conversion is always mathematically accurate.

Switching units in the middle of a design project

You can switch units at any point in your design without losing work. All sketches, bodies, and components convert automatically. However, if you have written down dimensions or shared measurements with someone else, those numbers will now be different. Before you switch, take a screenshot or note of any critical dimensions you need to reference later.

If you are working on a team project, talk to the other people involved before you switch. They may have the file open in the original unit system, and switching could cause confusion when you share the updated file. Many teams pick one unit system at the start and stick with it for the whole project to avoid this problem.

Mixing metric and imperial in the same design

Fusion 360 lets you use both metric and imperial measurements in a single sketch or design. You can type "2 inches" in one dimension and "50 mm" in another — Fusion 360 converts them to the same unit system automatically. This is useful when you are working with parts from different sources or suppliers that use different standards.

To use mixed units, type the measurement with its unit abbreviation. For example, type "2 in" for inches or "50 mm" for millimeters. Fusion 360 will convert it to your current unit system and show the converted number. This works in sketches, component properties, and anywhere else you enter a dimension.

Checking what unit system a file is using

If you open a file and are not sure what units it uses, go to File > Properties. The Units field shows the current system for that document. You can also look at the numbers in your sketches — if dimensions are in the hundreds or thousands, it is probably millimeters. If they are small decimal numbers, it is probably inches.

When you download a design from the internet or receive one from someone else, always check the units before you start working. A part that looks tiny in millimeters might be huge in inches. Taking 10 seconds to verify units saves you from building something the wrong size.

Units in Fusion 360 libraries and shared designs

When you save a design to the Fusion 360 cloud library or share it with a team, the unit system is saved with the file. Anyone who opens it will see the same units you used. If you want to share a design with someone who uses a different unit system, convert it to their units before you send it, or let them know what units the file uses so they can convert it themselves.

If you are using Fusion 360 in a team workspace, check whether the team has a standard unit system. Many organizations set a default — for example, all mechanical designs in millimeters, all architectural designs in feet and inches. Following the team standard makes it easier to share files and prevents mistakes when parts are assembled together.

Frequently Asked Questions

Does changing units affect the actual size of my 3D model?

No. Changing units only changes how the measurements are displayed. A part that is 100 millimeters wide is the same physical size as a part that is 3.94 inches wide. The geometry does not change, only the numbers you see.

Can I use inches and millimeters in the same sketch?

Yes. Type the unit abbreviation with your measurement — for example, "2 in" or "50 mm" — and Fusion 360 converts it to your current unit system. This works anywhere you enter a dimension.

What happens to my design if I switch units and then switch back?

Your design returns to the original numbers. If you switched from inches to millimeters and back to inches, a 10-inch dimension becomes 254 millimeters and then becomes 10 inches again. No information is lost.

Where do I find the units setting if I am using Fusion 360 on a Mac?

Go to Fusion 360 in the top menu bar, then select Preferences. Click Units in the left sidebar. The process is the same as on Windows, just in a different menu location.

Can I set different units for different parts in the same document?

No. All parts and sketches in a document use the same unit system. You can only change units at the document level through File > Properties or at the application level through Preferences.