Question 1

How do I open an STL file online?

Accepted Answer

Drag the file onto the STL viewer at the top of this page, or click Open file and choose it. It opens right in this browser tab, with nothing to install and no account to create. Binary and ASCII files up to 200 MB both work.

Question 2

How do I measure an STL file in mm?

Accepted Answer

Open it and read the Measurements panel: X, Y and Z size, surface area and volume. STL files store plain numbers without a unit, so the STL viewer reads them as millimetres, as most slicers do. Modelled in inches or centimetres? Pick that unit instead. GLB and glTF open in metres.

Question 3

How is the volume calculated?

Accepted Answer

The viewer adds up the signed volume of one tetrahedron per triangle, each running from the origin to that triangle. For a closed, watertight mesh this gives the exact enclosed volume; open meshes, holes or overlapping shells make the number unreliable.

Question 4

Can the STL viewer open 3MF, OBJ or GLB files?

Accepted Answer

Yes. It opens STL, 3MF (mesh geometry only: colours, slicer settings and plates are dropped and all objects merge into one mesh), OBJ, GLB, single-file glTF and PLY meshes. Point-cloud PLY files and glTF files that reference separate .bin or texture files won't open.

Question 5

Is my file uploaded?

Accepted Answer

No. The STL viewer reads the file and draws it on your own device with WebGL, and nothing is sent to a server. Confidential client parts stay on your computer, and you don't need an account to open, measure or screenshot them.

Question 6

Can I view GLB files with textures?

Accepted Answer

Yes. GLB and glTF open with their materials and textures as stored, so you can check a model from an AI 3D generator before converting it for printing. For GLB files, the dedicated GLB viewer adds a sample model and a GLB vs glTF comparison.

Question 7

Can I convert my STL to OBJ or GLB?

Accepted Answer

Yes. The free STL to OBJ converter makes an OBJ for Blender and other 3D apps, and the GLB to STL converter can also turn it into GLB or PLY. Both run in your browser like the STL viewer, so the file never leaves your device.

Question 8

Why does my model look dark, inside out or full of holes?

Accepted Answer

Usually the mesh has flipped normals or open edges. The viewer draws both sides of every triangle to keep the model visible; turn on wireframe to find gaps, and repair the mesh in Blender or your slicer's repair tool before printing.

Question 9

Can the STL viewer check if my model is watertight?

Accepted Answer

Not automatically: there is no watertight or manifold check. Turn on wireframe to look for gaps, and treat a volume that looks clearly wrong as a sign of holes or flipped faces. For a proper check and repair, use your slicer's repair tool or Blender's 3D-Print Toolbox.

Question 10

Can I use the STL viewer on an iPhone or Android phone?

Accepted Answer

Yes. Open this page in Safari or Chrome on the phone, tap Open file and pick your model. Drag with one finger to orbit and pinch to zoom; the measurements and PNG screenshot work the same as on a computer. Very large files may load slowly on older phones.

Free STL Viewer Online with Measurements

What the STL viewer shows you

How to view an STL file online

Open the file

Look around

Measure and share

An STL viewer online with measurement built in

Bounding-box size

Volume and surface area

Wireframe and grid

Opens 3MF, OBJ and GLB too

Screenshots

Private and free

STL viewer FAQ

More ways to work with your 3D files

GLB viewer

3MF to STL converter

GLB to STL converter

Image to STL

Have a photo instead of a model?