OneTaskBy Tim King · Updated
STL Viewer Online
Open STL Files for 3D Printing in the Browser, Free
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How the STL Viewer works
This STL viewer online needs no install or account. STL is the file every 3D printer and slicer understands: nothing but a list of triangles. Drop one on this page to see it in an orbit viewport, read its dimensions and triangle count, check it in wireframe for holes and flipped faces, pick a colour and download a PNG for a listing or a forum post. Both binary and ASCII STL files open, and neither is uploaded anywhere.
Opening a file in the STL viewer online
Drag the .stl file onto the drop zone or the viewport, or click to choose it. Binary STL, which is what slicers and most exporters write, and the older ASCII text form both load. The model appears in grey with a studio light and a ground grid; orbit with the left mouse button, zoom with the wheel and pan with the right. STL files are almost always saved with Z pointing up, so that is the default here; if a file comes in lying down, switch the Up axis menu to Y up.
Checking a model before printing
The triangle count in the rail is the first thing to look at. A few thousand triangles is a simple part, a few hundred thousand is a detailed figure, and several million is a raw scan that will slow the slicer down and gain nothing on the print. The size line gives width, height and depth in the file's units, which for printing should be millimetres: a phone stand that reads 2 × 4 × 6 was exported in inches or centimetres and needs scaling by 25.4 or 10 in the slicer. Switch Shading to Normals and look for patches in a different colour from their neighbours; those are faces pointing inward, which slicers treat as holes. Solid + wireframe shows where the mesh is dense and where it is coarse, and Wireframe on its own reveals internal geometry that a solid view hides.
Colour, lighting and screenshots
STL carries no colour, so the Model colour menu lets you pick one for the render. Lighting switches between a studio rig, soft flat light, a headlamp that follows the camera and unlit, and the background can be dark, light or white. Set auto-rotate on for a quick look from all sides, then stop it, frame the view and click Download PNG to save the image at preview, retina or 4K resolution. The render is made on your own graphics card and saved directly to disk.
Privacy
The file is read from your disk into the browser and never sent to a server. That matters for STL more than most formats, because printable parts are often unreleased products or paid designs. Once the page has loaded it works with the network off.
To measure the part, use the STL dimensions checker; for a clean square image for a listing, the STL thumbnail generator.
FAQ
Can this open both binary and ASCII STL files?
Yes. The page inspects the file to decide which form it is, so the extension alone does not matter. Binary files are much smaller for the same model, so if you have a choice when exporting, choose binary; an ASCII STL of a detailed model can be ten times the size.
Why is the model on its side?
Most STL files use Z as the up axis, which is the default here. A few exporters, particularly from game and animation tools, write Y up instead; switch the Up axis menu to Y up and the model stands correctly. The file is not changed, only the view.
What does the triangle count tell me?
How heavy the model is. Slicers cope with a few hundred thousand triangles easily but crawl above a few million, and the printer cannot resolve detail finer than its nozzle anyway. If the count is huge, decimate the mesh in the tool that made it or in a free program like Blender or Meshmixer, then check it here again.
Does the viewer check whether the model is watertight?
Not directly. It shows the mesh and lets you look for gaps in wireframe and for inverted faces in the Normals shading, which catches most problems, but it does not run a manifold check. Slicers and mesh repair tools such as Meshmixer or the free Windows 3D Builder do that and can usually repair the file automatically.
Are the dimensions shown in millimetres?
STL files have no units; the numbers are whatever the exporting program used. Most CAD and slicer software assumes millimetres, so a part that shows sensible millimetre values will print at the right size. If the values look a factor of ten or 25.4 out, the export was in centimetres or inches and the slicer's scale setting will fix it.
See also: all 3D Model Viewers tools, Images, Audio, Video & Screen, PDF, SVG, Simulations & Screensavers, Generative Art, Chart Makers, Drawing Pads, Mockups & 3D Making, Diagram Makers, 3D Science, Tracker Music.
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