STL Viewer Blog"Free" is doing a lot of work in most app store listings. Some free STL viewers turn out to be trials, some hide the size readout behind a paywall, and some want you to sign up and upload your model before you see it. If you are looking for a free STL viewer, it helps to know what a good one should do at no cost, so you can spot the difference in the first two minutes.
Below is a practical checklist, followed by an exact list of what STL Viewer for Android gives you free and what is in Premium, so there are no surprises.
Short answer: A decent free STL viewer should open STL plus at least one or two other print formats, work offline, show real dimensions and a watertight check, and never require an upload or an account. STL Viewer does all that free, plus a filament estimate; measuring, cross-sections, scaling/export and comparing are Premium.
The free STL viewer checklist
Run any viewer through these eight points. If it fails more than one or two, keep looking.
| # | Must-have | Why it matters for printing |
|---|---|---|
| 1 | Opens binary and ASCII STL | Older CAD exports and test files are often ASCII |
| 2 | Also opens 3MF, OBJ and ideally PLY | Slicer projects, colored models and scans |
| 3 | Works with no internet | Workshops and print rooms often have bad signal |
| 4 | No upload, no account | Client and paid files stay private |
| 5 | Shows width x depth x height | The first thing you need to know before printing |
| 6 | Lets you choose mm or inches | STL has no unit; US files are often in inches |
| 7 | Reports whether the mesh is closed | Open meshes cause slicer errors and gaps |
| 8 | Handles large files gracefully | Scans and sculpts can run to millions of triangles |
Nice extras: a print bed grid, wireframe and x-ray views, a filament or material estimate, recent files with thumbnails, and a dark theme for late sessions.
Red flags in "free" viewers
- Dimensions locked behind a purchase. Size is basic information; a viewer that hides it is a demo.
- Mandatory sign-in before you can open a local file.
- Upload on open, with no clear statement of what happens to the file afterward.
- Ads over the model, so you can't rotate without hitting one.
- A trial counter ("3 free opens left").
What STL Viewer gives you for free
Here is the free version, feature by feature, so you can check it against the list above:
- Formats: STL (binary and ASCII), OBJ with its MTL colors, 3MF with units, colors and multiple objects, and PLY (ASCII and binary). A ZIP with models inside opens the largest model.
- 3D view: one finger rotates, two fingers pan, pinch zooms, double-tap resets. Solid, wireframe and x-ray modes, a print bed grid and XYZ axes, your own model color or the file's colors.
- Model info: width x depth x height in mm or inches, triangle count, volume, surface area, file size, and a watertight check.
- Filament estimate: weight and length for PLA, PETG, ABS or TPU, 1.75 or 2.85 mm filament, infill from 0 to 100%.
- Recent files with thumbnails, the 10 most recent (older ones are hidden, not deleted).
- Offline and private: no account; models are read on the phone and never uploaded.
- Comfort: dark theme, a tablet layout with a side panel, and screen reader support.
The free version shows ads: a banner on the home list only, never over the 3D view, and an occasional full-screen ad when you close a model back to the list. You can get it by downloading STL Viewer from Google Play.
What Premium adds, and who actually needs it
| Premium tool | What it does | You need it if... |
|---|---|---|
| Measure | Tap two points for the distance plus X, Y, Z differences | You check hole spacing or fit against real parts |
| Section | Cut along X, Y or Z with a solid face, plus the cut's width, height and area | You print functional parts and care about walls |
| Scale & export | Scale by percent or to a target size, convert inches to mm, save binary STL | You resize models before sending them to the PC |
| Compare | Second model side by side with dimensions, volume and triangles | You review design revisions |
Premium also lifts the recent-file limit and removes ads. It is offered as a one-time purchase or a yearly subscription. If you only need to measure once in a while, you can watch a short ad for a single measurement without buying anything.
Example: what the free version tells you about a real file
Take a typical 20 mm calibration cube downloaded as an STL. The free info panel reports 20 x 20 x 20 mm, a volume of 8 cm³, a surface area of 24 cm², and "Watertight: Yes". With PLA, 1.75 mm filament and the default 20% infill, the filament estimate comes out at roughly 3.9 g and about 1.3 m. All of that is free and works in airplane mode. That is enough to answer the usual questions: will it fit, is the mesh sound, and is there enough left on the spool.
For the math behind that number, see how much filament your print will use.
When a free viewer isn't the right tool
No viewer, free or paid, replaces your slicer or a repair tool. If the watertight check says "No, it has holes or open edges", the fix happens in a mesh editor; our article on watertight meshes explains what to look for. And if your file is STEP, GLB or SCAD, you need to export it first; see which formats a phone viewer handles.
Note: The filament number is always an estimate. It assumes 0.8 mm walls and your chosen infill; supports, brims and slicer settings change the real amount.
A full feature list is on the STL Viewer website, and if you are just getting started, read how to open STL files on Android.
Frequently asked questions
Is there a completely free STL viewer for Android?
STL Viewer is free to download and use for viewing, dimensions, the watertight check and the filament estimate. The free version shows ads, and some advanced tools are Premium.
What should a free STL viewer show?
At least the model in 3D, its width, depth and height, a choice of mm or inches, and whether the mesh is closed. It should work offline and not require an upload.
What does STL Viewer Premium cost?
Premium is offered as a one-time purchase or a yearly subscription; the current price is shown in Google Play in your currency.
Can I measure for free?
Without Premium you can watch a short ad to take one measurement. Unlimited measuring is part of Premium.