Where to find the units setting in Fusion 360

Open Fusion 360 and go to the top menu. Click Preferences (on Mac) or Edit > Preferences (on Windows). A window will open with several tabs on the left side. Click the tab labeled Design. In the Design preferences, look for the section called Units. This is where you set whether your project measures in millimeters, inches, centimeters, or other standard units.

The units you choose here become the default for every new file you create. If you want to change units for only the current project — without affecting future files — you can do that from a different location, which we'll cover in the next section.

Changing units for your current project only

If you have a file already open and want to change its units without affecting your default settings, use the project-level setting instead. Click File > Project Settings at the top of the screen. A panel will open on the right side. Look for Units in that panel and select the unit system you want: metric (millimeters), imperial (inches), or another option depending on your region.

When you change units at the project level, Fusion 360 converts all your existing dimensions automatically. A part that was 100 millimeters long becomes approximately 3.94 inches if you switch to imperial. The geometry itself does not change — only how it is measured and displayed.

This project-level setting overrides your default preference for that file only. When you create a new file, it will use your default units from Preferences again.

Key Takeaways

  • Default units for all new files are set in Preferences > Design > Units, and this choice applies to every project you create going forward.
  • To change units for only the current file, use File > Project Settings and select a different unit system from the Units option.
  • Fusion 360 automatically converts all dimensions when you change units, so a 100 mm part becomes 3.94 inches if you switch to imperial.
  • The project-level setting overrides your default preference for that file only and does not affect future files.

Understanding metric versus imperial in Fusion 360

Metric units (millimeters, centimeters, meters) and imperial units (inches, feet) measure the same distances but use different scales. Fusion 360 treats them as separate unit systems, so you cannot mix millimeters and inches in the same sketch without converting one or the other first.

If you are working with parts designed in another country or from a supplier, check which unit system they used before you start. Importing a file designed in inches into a metric project can cause confusion and mistakes. Many manufacturers in the United States use inches, while most of Europe, Asia, and Australia use millimeters.

What happens when you import a file in different units

When you open a file that was created in a different unit system, Fusion 360 will ask you to confirm the units. A dialog box appears asking whether the file uses metric or imperial units. Choose the correct system — if you choose wrong, all dimensions will be scaled incorrectly and your part will be the wrong size.

If you accidentally import a file with the wrong units selected, undo the import (Ctrl+Z or Cmd+Z), then import again and choose the correct unit system. You cannot fix this by changing the project units afterward, because Fusion 360 has already baked the wrong scale into the geometry.

Changing units in sketches and drawings

When you create a sketch inside Fusion 360, it inherits the units from your project. If your project is set to millimeters, every dimension you draw will be in millimeters. If you change the project units after you have already sketched, all sketch dimensions convert automatically.

In technical drawings (the 2D views you create for manufacturing or documentation), the units also come from your project setting. When you add dimensions to a drawing, they display in whatever unit system your project uses. You cannot set drawing units separately — they are always tied to the project.

Common mistakes when switching units

The most common mistake is changing project units after you have already modeled a part, then wondering why it looks wrong. The part itself is fine — Fusion 360 converted it correctly. But if you have external references, imported parts, or files from collaborators, those may not convert automatically. Always check imported geometry after a unit change.

Another mistake is confusing the default preference with the project setting. Changing your default units in Preferences does not affect files you have already created. You have to change the project units separately for each existing file. Many people change their default, create a new file expecting it to use the new units, then forget that old files still use the old units.

Frequently Asked Questions

Can I use both millimeters and inches in the same Fusion 360 file?

No. Fusion 360 requires one unit system per project. If you need to work with parts in different units, convert one set to match the other before you start, or keep them in separate files and import them carefully.

What units does Fusion 360 use by default when I first install it?

The default depends on your region and language settings. Users in the United States typically get inches by default, while users elsewhere usually get millimeters. You can change this in Preferences > Design > Units whenever you want.

If I change project units, do my sketches and parts scale automatically?

Yes. When you change the project units, Fusion 360 converts all dimensions, sketches, and parts proportionally. A 100 mm cube becomes a 3.94 inch cube if you switch from metric to imperial.

What should I do if I imported a file and the units are wrong?

Undo the import when ready (Ctrl+Z or Cmd+Z), then import again and select the correct unit system. If you have already made changes to the file, you may need to delete it and start over, because Fusion 360 cannot retroactively fix a unit mismatch.

Can I see what units a file is using without opening it?

Not from the file browser. You have to open the file or check the project settings inside Fusion 360. If you are working with files from others, ask them directly what units they used, or check any documentation they provided.