SCAD to STL: Turn an OpenSCAD File into an STL You Can View

You found a customizable box, a parametric hinge or a cable organizer, and the download is a .scad file. You try to open it on your phone and nothing shows, because there's nothing to show yet: a .scad file is not a 3D model, it is a short program that describes one. To get from SCAD to STL, the code has to be rendered in OpenSCAD on a computer and exported. After that, checking and measuring the STL on your phone is easy.

What is a .scad file?

OpenSCAD is a free, open-source CAD program where you design by writing code instead of dragging shapes. A tiny example:

difference() {
  cube([40, 30, 15]);
  translate([2, 2, 2]) cube([36, 26, 15]);
}

That describes a 40 x 30 x 15 mm open box with 2 mm walls and a 2 mm floor. The file is a few hundred bytes of text. Nothing in it is a triangle; the geometry only exists after OpenSCAD runs the code.

That is why SCAD files are popular for customizable designs: the author exposes variables like width = 40; at the top, and you change them to fit your drawer, your phone or your screw size.

Why viewers can't open .scad

To display a .scad, a viewer would need to include the whole OpenSCAD language and its geometry engine, including libraries the file may include or use from other files on the author's computer. A viewer for printing files reads meshes instead. When you open a .scad in STL Viewer, it tells you SCAD files aren't supported yet and asks you to export the model as STL, OBJ or 3MF. Treat the .scad like a recipe and the STL like the cake.

How to turn a .scad into an STL, step by step

1. Install OpenSCAD on your computer (Windows, macOS or Linux) from its official site.
2. Open the .scad file. If it uses libraries (lines starting with include < or use <), put those library files where the readme says, or the render will fail.
3. Adjust parameters in the code, or in the Customizer panel if the author set one up. Change one thing at a time.
4. Preview with F5. It is fast but approximate; good for checking your changes.
5. Render with F6. This computes the real geometry. Complex models can take from seconds to many minutes.
6. Export with File > Export > Export as STL (or 3MF). F7 is the usual shortcut for STL export.
7. Name the file with the parameters you used, for example box_40x30x15_w2.stl.

OpenSCAD has no built-in units, but the community convention is millimeters, and slicers assume millimeters too, so 40 in the code becomes 40 mm in the print.

Tips for smoother renders

• Curve resolution is set with $fn. $fn = 32 gives a 32-sided circle; $fn = 128 is smoother and slower. For a 5 mm hole, 32-48 sides is plenty for FDM.
• Huge $fn values on many spheres or minkowski() operations can make F6 take a very long time. Lower them, export, check.
• If F6 reports errors about non-manifold geometry, the model will probably also fail the watertight check later; fix it in the code first.

Check the exported STL on your phone

Once the STL exists, send it to your phone through your cloud folder, email or a USB cable, and open it in STL Viewer for Android. Then compare what you asked for with what you got:

For parametric parts that must fit something real, Premium's Measure tool lets you tap the inside walls of the box, for example, and confirm 36.0 mm between them before printing. The measure guide explains it.

Worked example: a customizable drawer divider

You download a .scad divider with length = 150; height = 40; thickness = 2;. Your drawer is 182 mm wide, so you set length = 180, press F6, export STL and send it to your phone. The info panel shows 180 x 2 x 40 mm, "Watertight: Yes". Your bed is 220 x 220 mm, so it fits flat. In PLA at 20% infill the filament estimate is about 16 g and roughly 5 m of 1.75 mm filament. Infill barely matters here: a 2 mm wall is almost all shell, so 0% or 100% infill would only move the number by a gram or two. Print one, test it in the drawer, then come back to the code for the other dividers. For how that estimate is built, see how much filament your print will use.

Comparing two parameter versions

If you render the same .scad with two different settings, say a 2 mm and a 2.4 mm wall, Premium's Compare opens the second STL next to the first and lists dimensions, volume and triangles side by side, so you can see the material difference before you print either. Background on mesh quality is in what watertight means, and for other source formats see STEP vs STL.

The STL Viewer website lists every format the app reads, so you know what to export.