# Mes3D Blog

> Practical guides on opening, inspecting and preparing 3D models: file
> formats, volume and print weight, watertight meshes and printability.

Source: https://freestlviewer.com/blog/

## Articles

- [How to Open an STL File (Windows, macOS, Linux and the Browser)](https://freestlviewer.com/blog/how-to-open-stl-files/): An STL file is a plain mesh of triangles, so almost anything can display it. Here is the fastest way to open one on each operating system, and what to do when the model looks wrong.
- [How to Calculate the Volume and Print Weight of an STL File](https://freestlviewer.com/blog/stl-volume-and-print-weight/): Mesh volume comes from summing signed tetrahedron volumes over every triangle. Multiply by material density to get weight. Here is the maths, the unit trap and why the number is an upper bound.
- [Watertight and Manifold STL Files: What They Mean and How to Check](https://freestlviewer.com/blog/watertight-and-manifold-stl-files/): A watertight mesh has every edge shared by exactly two triangles. Here is why STL makes that hard to verify, how the check actually works, and how to repair a mesh that fails it.
- [STL vs OBJ vs PLY vs glTF vs 3MF: Which 3D Format Should You Use?](https://freestlviewer.com/blog/stl-vs-obj-vs-ply-vs-gltf-vs-3mf/): STL carries geometry only, 3MF adds units and colour for printing, glTF is built for real-time rendering, OBJ for interchange and PLY for scans. A practical comparison with a decision rule for each.
- [STL Files Have No Units: Diagnosing and Fixing Scale Problems](https://freestlviewer.com/blog/stl-units-mm-vs-inches/): An STL stores bare numbers, so the unit lives only in the exporting program's settings. Here are the exact scale factors to look for and how to fix a model that opens 25.4 times too small.
- [Overhang Angle and When You Actually Need Supports](https://freestlviewer.com/blog/overhang-angle-and-supports/): The 45-degree rule comes from each layer needing roughly half its width supported by the layer below. Here is where the rule holds, where it breaks, and how to avoid supports by design.
- [A Pre-Print Checklist for 3D Models](https://freestlviewer.com/blog/pre-print-checklist/): Nine checks that catch most failed prints before they start: scale, fit, watertightness, wall thickness, overhangs, orientation, clearances, small features and material estimate.
- [Filament and Resin Density Reference (and How to Convert Volume to Grams)](https://freestlviewer.com/blog/filament-density-reference/): Typical densities for PLA, PETG, ABS, ASA, TPU, nylon, PC and resin, plus the formulas for converting mesh volume to grams and a spool's weight to metres of filament.
- [Binary vs ASCII STL: The Difference, the Sizes and the 'solid' Trap](https://freestlviewer.com/blog/binary-vs-ascii-stl/): Both variants describe identical geometry. Binary uses 50 bytes per triangle, ASCII about six times more. Here is the byte layout, when to use each, and why some binary files start with the word solid.
- [Triangle Count, Resolution and File Size: How Fine Should Your Mesh Be?](https://freestlviewer.com/blog/triangle-count-and-file-size/): A binary STL is exactly 84 + 50 × N bytes, so triangle count and file size are the same number. Here is how export tolerance drives that count and where extra triangles stop buying you anything.