3D Model Converter

Most problems after a 3D conversion are not about the shape but about size and direction. STL and OBJ store coordinates as bare numbers, so a value of 10 might mean 10 millimeters, 10 inches or 10 meters depending on who made the file. Slicers usually assume millimeters, game engines often assume meters, and some modeling tools work in centimeters. A model that arrives a thousand times too small has usually been read in the wrong unit, not damaged.

Model units tells the converter what the numbers in your source mean: millimeters, centimeters, meters or inches. Formats that store units, such as 3MF, glTF and STEP, then get the right value written into them. The glTF specification is strict on this point and defines every distance in meters, so a printer model in millimeters is scaled correctly on the way into GLB when the unit is set.

Orientation works the same way. glTF defines +Y as up, as do most game engines, while CAD programs and slicers usually treat Z as up. A model exported from one world and opened in the other appears tipped onto its back. Up axis set to Keep leaves the coordinates alone, while Y-up and Z-up rotate the model so it stands the way the target program expects.

For printing, the choice between STL and 3MF comes down to what your slicer and printer do with the extra information. STL is accepted by every slicer and is fine for a single-color part. 3MF, defined in the consortium's 3MF specification, carries the unit with it, so the part arrives at the right size without guessing, and it can keep colors, materials and several objects on one plate, which matters for multi-material printers. If your slicer reads 3MF, it is the safer format to hand to someone else.

File encoding applies to STL, PLY and FBX. Binary files are compact and load quickly, which is what slicers and engines prefer. ASCII writes the same geometry as readable text, several times larger; choose it only when a program or a script specifically asks for text input.

Open the converted file in its target program before you print or publish it. A quick look at the dimensions in a slicer, or at the model standing upright in an AR viewer, catches unit and axis mistakes in seconds.

Every format on the list stores a surface as a mesh of triangles, except STEP, which can describe exact curves and solids. Converting from STEP or another solid format to a mesh means approximating curved surfaces with flat facets. Mesh detail sets how fine those facets are: Coarse gives a light file that suits previews and the web, Fine keeps round parts smooth for printing at the cost of a much larger file, and Normal sits between them. Going from a mesh back to STEP keeps the facets, so the result opens in CAD but is not a parametric model you can edit by feature.

Textures and materials travel only where the target can hold them. Keep textures & materials is on by default for OBJ, GLB, glTF, FBX, 3MF, USDZ, DAE and PLY. STL cannot store any of it, so a colored model saved as STL comes out as a single plain shape. For an OBJ with an MTL file and texture images, add all the files together, or pack them into one ZIP, so the converter can find them. Merge into one mesh joins separate parts into a single object, which some slicers and AR viewers handle better than a model made of many pieces.

If a model will not slice or shows holes after converting, the source mesh probably had gaps or flipped faces already; conversion keeps the geometry as it is and does not repair it. A slicer's repair function or a mesh editor is the place to fix that.

For models that will be viewed on a web page or in AR, file size decides how long people wait before anything appears. A GLB at Coarse or Normal detail with textures at a sensible resolution usually loads far faster than a print-ready mesh. Keep a fine version for printing and a lighter one for the web, rather than trying to make a single file serve both purposes.

PNG, JPG, SVG, BMP and WebP images can be turned into printable models with the options above. A clean, high-contrast image gives the best relief or extrusion; for a lithophane, a well-lit portrait with soft gradients works better than a dark or very busy photo. Lithophanes are usually printed upright in white filament so the layers follow the picture, and the thinnest parts become the brightest, so keep Base thickness high enough that the panel does not break. If the picture needs a different size, crop or format first, the image converter handles that, and for flat drawings that should become DXF lines for a cutter rather than a 3D solid, use the CAD converter page.

When a project contains many parts, such as a multi-file OBJ or a print plate split into pieces, the Zip Files tool keeps them together for sending. Other converters for less common file types sit under more tools.