Free STL viewer for Android and Windows

Updated 16 October 2026 By the tool room at Saptasati Industries 3 min read

STL is the 3D-printing format: a list of triangles covering the surface of a part. It is perfect for checking shape, orientation and printability before you print, and it opens anywhere. What it cannot carry is exact circles, edges or units, so numbers measured on an STL are always approximations, whichever app you use.

What PartLens does with an STL file

• Binary and ASCII STL, including a file cut short by a broken download, which still shows the triangles that arrived.
• Smooth shading with sharp edges kept, so a printed part looks like a part, not a pile of facets.
• Sections through the mesh, to check wall thickness and internal channels.
• Approximate measurement (≈) of distances and sizes between points on the mesh.

Open an STL file

1. Get PartLens free from Google Play or as a Windows download.
2. On Android: Tap the file in WhatsApp, Gmail, Drive or your file manager and choose PartLens under Open with, or open PartLens and tap Open.
3. On Windows: Install the free Windows app, then double-click the file, drag it onto the window, or use Open CAD….

Nothing is uploaded: the file is read on your device, with no account.

STL has no units

An STL file does not say whether its numbers are millimetres or inches. PartLens reads them as millimetres, the usual convention for 3D printing. If a part looks 25.4 times too small, it was exported in inches.

When to ask for a STEP instead

For inspection, quoting or tooling, ask for a STEP file: it carries exact geometry, so hole diameters and positions are real numbers. You can always make an STL from a STEP, never the reverse.

Frequently asked questions