Converted locally
OpenCascade runs in your browser as WebAssembly, so your IGES file stays on your computer.
IGES to STL Converter for 3D Printing
Turn .igs and .iges files from CATIA, NX, SolidWorks or Rhino into a binary STL at real size, as one file or one per part, right in your browser.
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Converted in your browser. Files are never uploaded.
Continue with your model
Check the IGES file for gaps, or prepare the STL parts for your slicer.
How to convert IGES to STL
- 1
Add your IGES files
Drop .igs or .iges files, one or many. The CAD reader downloads once, with the first file.
- 2
Check size and parts
The size comes from the unit in the IGES header, shown in millimeters. Resize the longest side if you need to.
- 3
Download the STL
Save a binary STL per file, or a ZIP with one STL per solid or surface set, on the build plate.
Why use this IGES to STL converter
For IGES models that need to end up on a 3D printer.
Surfaces and solids
Reads B-rep solids and trimmed NURBS surfaces alike, the two ways CAD programs write IGES.
Unit from the header
Inch, millimeter and meter files all come out in millimeters, the unit slicers expect.
One STL or one per part
Merge everything into one STL, or download a ZIP with one STL for each solid or surface set.
What carries over from IGES to STL
IGES stores exact curves and surfaces. STL stores only triangles, so the shape and the size come through and the rest stays behind.
Kept
- Solids, shells and trimmed surfaces
- Where every entity sits in the model
- Real size, converted to millimeters
- Solid names, as file names when split
Left behind
- Exact NURBS geometry, replaced by triangles
- Colors, layers and levels
- Loose curves, points and annotations
- Gaps between surfaces, which are not closed for you
Four checks before you slice
IGES files are often surface models, so check that yours will print as a solid.
Watertight check
Surface exports can leave open edges. Open the file in the IGES viewer first; if it reports hundreds, export a solid or STEP instead.
Real size
Compare the size with your build plate. If an old file has the wrong unit in its header, the part comes out 25.4 times too big or small.
Single surfaces
A lone surface has no thickness, so a slicer cannot fill it. Thicken sheet-like surfaces in CAD before you export.
A flat base
The converter keeps the CAD orientation and puts the lowest point on the plate. Turn the part in the slicer so a flat face sits down.
IGES to STL guide
Formats, tessellation, surface models, units and files that will not convert.
IGES, STEP and STL compared
IGES and STEP both describe exact CAD geometry: curves, NURBS surfaces and, when the exporter supports it, closed solids. STL describes only a surface of triangles, with no unit, color or structure, and slicers read it as millimeters.
IGES is the oldest of the three and the one most often used for surface models, which matters for printing, as the next sections explain.
Geometry
- IGES
- Exact curves and surfaces
- STEP
- Exact solids and surfaces
- STL
- Flat triangles
Solids
- IGES
- Optional, entity type 186
- STEP
- Standard
- STL
- Closed if watertight
Units
- IGES
- Unit flag in the header
- STEP
- Stored in the file
- STL
- Not stored, read as mm
Color
- IGES
- Per entity
- STEP
- Per part and per face
- STL
- None
First published
- IGES
- 1980
- STEP
- 1994
- STL
- 1987
Tessellation: turning surfaces into triangles
The surfaces in an IGES file are exact. A slicer needs triangles, so each surface is tessellated: covered with triangles whose corners lie on it. Curved areas need many small triangles to follow the shape, and flat areas need only a few, with no loss at all.
The converter lets a triangle stray from the true surface by at most 0.05 percent of the model's average size, which is 0.05 mm on a 100 mm part, and also limits the angle between neighboring facets so small holes and fillets stay round.
Surface IGES and solid IGES
IGES can store a model in two ways. Trimmed surfaces (entity type 144) are separate faces that only look joined; each face is tessellated on its own, so seams between faces may not line up and the STL has small open edges. A manifold solid (entity type 186) stores faces that share their edges, and it tessellates into a closed, watertight mesh.
If the IGES viewer reports open edges, export again as a solid or as STEP, or join the surfaces into a closed body in your CAD program first, for example with Join in Rhino or Knit Surface in SolidWorks. Slicers can also close a few small gaps on import.
Units in the IGES header
The global section at the top of an IGES file stores a unit flag, and the converter scales by it so the STL is in millimeters. The common flags are below.
A file with a wrong flag still converts, just at the wrong scale. Fix it with Resize longest side, or correct the unit in the program that exported it.
1
- Unit
- Inch
- One unit in the STL
- 25.4 mm
2
- Unit
- Millimeter
- One unit in the STL
- 1 mm
4
- Unit
- Foot
- One unit in the STL
- 304.8 mm
6
- Unit
- Meter
- One unit in the STL
- 1000 mm
10
- Unit
- Centimeter
- One unit in the STL
- 10 mm
When an IGES file will not convert
If you see No triangles found, the file holds only lines, arcs and points, which is common for 2D drawings exported as IGES. There is no surface to turn into triangles. For a flat outline you want to extrude, save a DXF and use DXF to STL instead.
If the file cannot be read at all, it may be cut short or not follow the 80-column layout, for example after it was edited in a text editor that rewrapped the lines. Export it again from the original program. Files up to 300 MB are accepted.
IGES to STL questions
Answers about gaps, supported files, accuracy, units and privacy.
Why does my STL have holes after converting an IGES file?
The IGES file was most likely saved as separate surfaces. Each surface is turned into triangles on its own, so seams may not line up. Export a solid IGES (type 186) or a STEP file, or let your slicer repair the small gaps.
Which IGES files can it convert?
Files with surfaces or solids, in .igs or .iges: trimmed NURBS surfaces, shells and B-rep solids. Files with only lines and curves, such as 2D drawings, have no surface to turn into triangles.
How accurate is the conversion?
Curved surfaces become triangles that stray from the true shape by at most 0.05 percent of the model's average size, which is 0.05 mm on a 100 mm part. Flat faces are exact.
Does it keep the unit of my IGES file?
Yes. The unit flag in the global section, whether inches, millimeters, feet or meters, is converted, so the STL comes out in millimeters.
Is the IGES to STL converter free and private?
Yes. It is free with no sign-up, files up to 300 MB are accepted, and the conversion runs in your browser without uploading anything.