STL viewer online with dimensions

An STL viewer shows a model in your browser with nothing to install. STL is the most common 3D printing format: it describes a part's surface as a mass of triangles. There's no color, material or unit in it, only geometry, so a downloaded or shared STL is worth a quick look before printing.

Everything happens in your browser and the file is never uploaded, so you can safely open a client's part or your own unreleased design.

Typical reasons to open an STL file without a slicer:

• a quick look at a model from a download site before firing up the slicer;
• checking an STL someone sent to your phone when you're away from your computer;
• confirming size and volume before quoting a job;
• deciding whether the mesh is broken and needs repair;
• finding out whether the model fits your printer's bed.

After loading you'll see:

• Size X × Y × Z: the bounding box edges in mm or inches.
• Volume in cm³ or in³, using the signed tetrahedron method: each triangle forms a small tetrahedron with the origin, and on a closed mesh their signed sum is exactly the solid's volume.
• Surface area in cm², the sum of all triangle areas.
• Triangle count and number of separate bodies.
• Watertightness: whether the mesh is closed, and if not, where it's broken.

On the Measure tab, click two points on the surface to get the distance plus ΔX, ΔY and ΔZ, so you can check a hole position or a tab's thickness. On the Section tab, a slider cuts the model horizontally (Z) or along X or Y. The inside shows in red, revealing wall thickness and any hidden cavity.

Worked example: a 20 mm calibration cube has 12 triangles. Its volume is 20 × 20 × 20 = 8,000 mm³ = 8 cm³ (about 0.49 in³), and its surface area 6 × 400 mm² = 24 cm². Solid PLA (about 1.24 g/cm³) would weigh roughly 9.9 g, but your slicer prints walls and partial infill, so the real filament use is lower.

STL comes in two flavors, and this viewer opens both. The format is detected from the file's contents.

	Binary STL	ASCII STL
Structure	80-byte header, triangle count, 50 bytes per triangle	text: "facet normal … vertex …"
100,000 triangles	about 5 MB	several times larger
Readable in a text editor	no	yes
When to use it	almost always	debugging, hand editing

A known trap: some programs write "solid" into a binary STL's header. That's the keyword ASCII files start with, so some viewers mix the two up and show a blank screen. This viewer also checks the file size to tell which is which. If you pass a model around a lot, binary STL or 3MF is the better choice.

STL stores bare numbers with no unit. Slicers read them as millimeters, and most models are made that way. If a model looks suspiciously tiny or huge, it was probably saved in a different unit:

What you see	Likely cause	Factor to mm
25.4 times smaller than expected	designed in inches	× 25.4
10 times smaller	saved in centimeters	× 10
1,000 times smaller	saved in meters	× 1,000

Set the file unit in the viewer and every value updates at once. The display unit can be switched separately between mm and inches.

Watch the volume: it changes with the cube of the factor. A model saved in inches but read as millimeters looks 25.4³, or about 16,387 times, smaller in volume. Example: a 3 × 2 × 1 inch box is correctly 76.2 × 50.8 × 25.4 mm; with the wrong unit it becomes a 3 × 2 × 1 mm crumb.

On the Print tab, pick your machine from about two dozen preset printers (Bambu Lab, Prusa, Creality, Elegoo, Anycubic, Qidi, Voron, plus a few resin printers). You'll see:

• whether the model fits, doesn't fit, or fits only when rotated 90°;
• the largest scale at which it still fits;
• one click to scale it to 98% of the bed, or any percentage you enter;
• a download of the resized model as STL or 3MF.

Overhangs are shaded orange. Set the threshold anywhere from 30° to 75° (45° by default); faces resting on the bed don't count. The overhanging area is shown in cm², so you can tell whether supports are needed in this orientation.

From the material (PLA, PETG, ABS, ASA, TPU, nylon, PC, PLA-CF), infill, wall count and average flow, you also get a filament and print time estimate. It's a rough estimate; your slicer gives the exact number. For cost, continue to the 3D print cost calculator.

The watertightness check looks at how edges connect after coincident vertices are merged. In a clean, printable mesh every edge belongs to exactly two triangles. Bad edges are highlighted in red in the 3D view.

• Open edge (hole): only one triangle uses it. The slicer can't tell where the inside is.
• Non-manifold edge: more than two faces meet, for example two bodies touching along an edge.
• Flipped normal: neighboring faces point in opposite directions.
• Inside-out shell: every face points inward, so the volume comes out negative.
• Zero-area triangle: a degenerate face, usually harmless.

If errors turn up, fix the mesh right away on the Repair tab. The STL repair page explains each error and the repair steps in detail.