Use reductions carefully
Keep your original STL and compare simplified copies around curved surfaces, small features and fitting areas before slicing.
STL file optimisation
STL File Size Reducer
Reduce a local STL by converting ASCII to compact binary, or create a carefully simplified copy.
Choose an STL file
Choose an STL file to optimise locally.
ASCII and binary STL files up to 25 MiB are supported.
An STL compressor can mean binary encoding or triangle simplification. Simplification can reduce visible detail and is not lossless.
Your STL stays in your browser.
Try an example
Does an unchanged bounding box preserve a small ridge?
Settings: Reducer: triangle reduction at 75%. Compare: original coordinate frame, mm on both sides, 0.1 mm tolerance, 5,000 samples per direction.
Downloads this public control, then opens it locally. Your own file can still be chosen above.
Read the explanation · Download and compare controls · Methods and processing
Choose encoding or geometry reduction
Understand chord deviation before reducing a curved export.
Binary encoding rewrites triangle records compactly; it does not intentionally remove triangles. The binary size is 84 + 50N bytes for N triangles: a 12-triangle cube is 684 bytes. ASCII size depends on decimal formatting and whitespace. Re-encoding uses binary floating-point coordinates, so recheck precision-sensitive data rather than treating a format change as restoration of source CAD accuracy.
Triangle reduction changes the surface. The presets request 75%, 50% or 25% of the source triangles; the custom target requests a count below the original. A target is a simplification request, not a feature-preservation contract. Results should be judged by the actual output count, bytes, bounds, mesh findings and surface deviation, rather than whether a preferred percentage was reached.
Verify a smaller export
A second owned control adds a curved wall and a small recessed key. The original has 512 triangles and 25,684 bytes. The independently generated 75% and 50% candidates reopen with 384 triangles / 19,284 bytes and 256 triangles / 12,884 bytes respectively. The 75% copy retains 20 x 20 x 10 coordinate spans; the 50% copy measures approximately 19.975908 x 19.987954 x 10, shrinking X by 0.024092 and Y by 0.012046 coordinate units. Bounds alone cannot establish preservation of the key or curvature. These are observed software outputs, not physical print results.
- Original curved control
- Actual 75% candidate
- Actual 50% candidate
- Exact bytes, bounds, versions and reproduction
Compare the original triangle projection with the 50% projection at the same scale and view. These projections are generated from the saved triangle records, not screenshots. Reopen both files above and inspect the key at the same zoom before accepting either derivative.
- Keep the original and confirm its units and functional dimensions.
- Try encoding first if text overhead is the problem.
- For geometric reduction, start with the least aggressive useful target.
- Download, reopen, inspect contact faces and check closure and winding.
- Compare against the original using an explicit surface tolerance.
The raised-ridge example and its reduced exports demonstrate why unchanged bounds cannot protect small details. Use that worked comparison instead of assuming a smaller file prints the same. Stop when a required feature changes or a topology check regresses; return to the source export settings. Processing on this page is local to the browser; a failed parse or unavailable simplification result is an error, not zero geometry.