# How to prepare an STL file for 3D printing

> Closed geometry, correct units and suitable wall thickness: how to prepare a printable STL file and avoid common problems.

Canonical: https://printimir.ch/en/guides/prepare-stl-file-for-3d-printing

## How to prepare an STL file for 3D printing

An STL file describes only the surface of your model as a triangular mesh. A few checks before upload determine whether it can become a clean print.

### Closed geometry

The model must be a watertight solid, not an open collection of surfaces. Holes, duplicate faces and reversed faces cause preparation errors. Most CAD and modelling applications can inspect and repair a mesh. Use that function before exporting.

### Units and size

STL does not store a unit. Export in millimetres and check the size in the preview after upload. A model that suddenly appears ten times too large or too small was usually exported in the wrong unit. You can correct it with scaling in the configurator.

### Wall thickness

Very thin walls cannot be printed reliably. As a guide, walls should be at least 1 mm thick (absolute minimum 0.8 mm); load-bearing walls and freestanding details are better at 1.2 mm or more. Delicate points and extremely thin edges may break or fail to print.

### Overhangs and supports

Steep overhangs require support structures in FDM printing. We remove them and include them in the print time. If you can orient or split the model to need fewer supports, the print will generally be cleaner and less expensive.

### Details that may disappear

Raised or recessed text less than 0.6 mm deep or with strokes under 0.8 mm often becomes unclear in FDM printing; around 1 mm of depth is on the safe side. Make text and fine patterns more generous or choose a finer layer height.

### Frequently asked questions

#### Does the STL need to be print-ready?

A closed, correctly scaled model gives the most reliable calculation. We can often repair small issues; larger ones require reworking.

#### Which formats can I upload besides STL?

STL, OBJ, 3MF, STEP and STP. STEP comes directly from CAD and does not need to be converted to STL.

#### Will my file remain private?

Yes. Uploaded customer files are not used as public content.

### Read next

[Print an STL file](https://printimir.ch/en/print-stl-file) · [Print a STEP file](https://printimir.ch/en/print-step-file) · [Upload a model](https://printimir.ch/en/3d-printing/upload-model) · [All guides](https://printimir.ch/en/guides)

### Ready?

Upload your model and see the price instantly, or describe your project if you do not have a file yet.

[Upload model](https://printimir.ch/en/3d-printing/upload-model) · [Request a project](https://printimir.ch/en/3d-modeling/request)