3MF viewer: open 3MF files without a slicer

3MF (3D Manufacturing Format) is the newer file format for 3D printing. Under the hood it's a ZIP package: the mesh is stored as XML, with other files alongside it. Compared with STL it has several advantages:

• it records the unit, so nobody has to guess whether the model is in millimeters or inches;
• it can hold several objects in one file, along with their positions on the plate;
• it can describe color and material;
• it's compressed, so the same model is smaller than a binary STL;
• slicers save their projects in it: settings, plates, painted colors.

This 3MF viewer shows you what's in the file without a slicer. Everything runs in your browser; the file is never uploaded. It's handy when someone sends you a project on your phone, when you're at a computer without your slicer, or when you just want to check the size of a downloaded model.

Slicers produce two kinds of 3MF, and it helps to tell them apart:

File	What's inside	Where to open it
Project: name.3mf	models, layout, settings	here, in the 3MF viewer
Sliced: name.gcode.3mf	ready G-code for each plate, preview image	in the G-code viewer
Plain model 3MF (model sites, CAD)	one or more meshes, sometimes color	here

A sliced file (what Bambu Studio and OrcaSlicer export as a plate) holds printer instructions per plate, not a model. The G-code viewer unpacks it, lets you pick a plate, and shows the toolpath layer by layer.

From a project file, this viewer shows the geometry. The slicer's own data, such as the print profile, filament assignments, hand-painted colors or support painting, lives in separate slicer config files inside the package. Those aren't displayed, so a model painted in several colors usually shows up here in a single color.

• Every object in place, as arranged in the file. If the file stores color as standard 3MF materials or color groups, you see that too.
• Size X × Y × Z for the whole contents, in millimeters or inches.
• Volume in cm³ or in³, surface area and triangle count.
• Number of separate bodies: in a multi-object project, this tells you how many parts are in the file.
• Mesh check: open edges, non-manifold edges, flipped and zero-area faces, inside-out shells. Bad edges are highlighted in red.
• Measure between two points, with ΔX, ΔY and ΔZ.
• Section along Z, X or Y, so you can check wall thickness and hidden cavities.
• Screenshot as PNG.

3MF treats Z as up, so models appear standing upright. If the size still looks off, you can set the file unit by hand.

A project 3MF often holds a full plate, say four parts side by side. Size and bed fit then refer to the bounding box of the whole layout. If the layout doesn't fit, the individual parts may still fit one by one; check that in your slicer by arranging them.

Volume and surface area are totals across all bodies, which is useful for a rough material estimate for a whole plate. Example: a file has four identical brackets of 12 cm³ each. The viewer shows 4 separate bodies and 48 cm³ (about 2.9 in³). Solid PLA (about 1.24 g/cm³) would weigh roughly 60 g; printed with walls and infill it will be less. On the Print tab you get an estimate in grams and meters from the material, infill and wall count.

If two objects overlap, the mesh check doesn't flag it as an error. The slicer merges them when it prints.

On the Print tab, pick your machine from about two dozen preset printers. You'll see whether the model fits, fits only when rotated, and the largest scale that still fits. One click scales it to 98% of the bed, and you can then download it as STL or 3MF. Overhangs are shaded orange, with an adjustable angle threshold.

The downloaded 3MF contains geometry only, not slicer settings. If the mesh has errors, fix them on the Repair tab and save the repaired model as STL or 3MF as well.

If you need another format, such as STL for an older slicer or GLB for a website, use the 3D file converter. It works the other way too: when you send a model to someone, 3MF beats STL because the unit and the object layout come along.