Do I need an internet connection?

No. After the first download from the App Store the app is fully offline. STL files are parsed on-device and never uploaded.

Does it support AR view?

Yes. STL files can be viewed at real-world scale using iOS Quick Look AR — place the model on a table or floor and walk around it.

Is there a size limit?

Recent iPhones (iPhone 12 and up) comfortably handle STL files up to about 100 MB. Older devices may struggle above ~40 MB.

Does it cost anything?

No. Open3D Viewer for iPhone is free, ad-supported, and no in-app purchases are required to open STL files.

iOS · iPadOS

STL viewer for iPhone.

Open .stl files directly on iPhone or iPad. Downloads from Thingiverse, MakerWorld, Printables. Attachments from Gmail, Outlook, Messages, WhatsApp. Files saved to iCloud Drive. All open in Open3D with one tap — no signup, no upload, no cloud round-trip.

Download on App Store → All formats & platforms

What you can do with it

Open ASCII and binary STL files from the Files app, Mail, Messages, or any browser download
Orbit, pan, zoom with one and two finger gestures
Measure point-to-point in mm, cm, or inches
Cross-section any axis to inspect internal geometry before you slice
Solid, wireframe, X-ray render modes
Screenshot the model for chat / email / a Slack thread
AR view via Quick Look — place the print at real scale on your desk before you commit filament

Why open STL on iPhone rather than a laptop

Most STL downloads happen on the couch. You're browsing MakerWorld on your phone, you find a print that looks interesting, and you want to check if it's actually the right size and printable before you send it to your printer's slicer.

Before Open3D, the answer was: forward the link to your laptop, boot up the slicer, wait. Now you tap the .stl in Safari, choose Open with Open3D, and the model appears in about a second. Measure the base to make sure it fits your build plate. Section through it to see internal supports. Then send it on to your slicer of choice.

Privacy: nothing goes to the cloud

iOS enforces sandboxed file access, so an STL you open in Open3D is only ever readable by Open3D — not by Apple, not by us, not by any of the ad networks that fund the free tier. The STL parser runs entirely on-device. There are no network calls related to the file. You can verify this yourself in Settings → Privacy & Security → App Privacy Report.

FAQ

How do I open a .stl file on iPhone?

Install Open3D Viewer from the App Store, then tap the .stl in the Files app (or Mail, Messages, WhatsApp, Drive) and choose Open with Open3D. It opens instantly. You can also set Open3D as the default handler for .stl in Settings → Files.

Does it work offline?

Yes. After the first App Store download the app is fully offline. STL files are parsed on-device with no server round-trip.

Can I use AR to preview the print at real size?

Yes. Tap the AR icon — Open3D hands the model off to iOS Quick Look AR, which lets you place it on a table or floor at real-world scale. Useful for checking whether that vase will actually fit on your shelf before you print it.

What's the biggest STL file it can handle?

Depends on the device. iPhone 12 and up: ~100 MB comfortably. Older devices: closer to 40–60 MB. If a file fails to open, decimate it in a desktop tool first (Meshmixer, Blender, or the on-device decimator we're shipping in a later release).

Is it free?

Yes. Free, ad-supported. Ads run outside the model viewport and never obscure your file. No in-app purchases are required to open any format.