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How to Open a STEP File
View it free in your browser, open it in CAD or convert it to STL
A STEP file (.step or .stp) holds a 3D solid model, and most computers ship with no app that opens one, so double-clicking it does nothing. The fastest way to open it is to drag it into a free browser viewer, with no install and no account. To edit it, open it in CAD software: FreeCAD, SolidWorks and full AutoCAD on Windows all import it.
Short answer: open it in the free STEP file viewer — upload the file and it renders in your browser. The rest of this page covers CAD, AutoCAD, and converting the file.
How do I open a STEP file without installing anything?
Drag it into a browser viewer. The part renders in seconds and you can orbit, zoom and measure it on a desktop or a phone. With PartWork.ai viewing is free and needs no account, so you can confirm you have the right part before doing anything else.
Open the studio
Go to studio.partwork.ai in any modern browser.
Upload your .step / .stp file
Drop the file in or pick it from your computer. It loads as a 3D model you can rotate and zoom.
Inspect — or convert
Orbit and view it free. When you want a copy in another format (STL for printing, for example), sign up free to download.
See importing files for the supported formats.
Are .step and .stp the same file?
Yes. .step and .stp are the exact same format; the three-letter .stp spelling exists only because old Windows software limited file extensions to three characters. If a program opens one, it opens the other.
Curious what is actually inside? See what is a STEP file.
Which CAD programs open STEP files?
Nearly all of them. STEP is a neutral format, so FreeCAD (free), SolidWorks, Fusion, Onshape, Inventor and full AutoCAD on Windows all read .step and .stp files, usually through File → Open or Import. The CAM software at machine shops reads it too.
The trade-off is that these are heavy installs or paid seats with a real learning curve, which is overkill if you only need to look at the part or pass it to a shop.
How do I open a STEP file in AutoCAD?
Use the IMPORT command, not Open: Open only reads drawing files such as DWG and DXF. This works in full AutoCAD on Windows, which reads the common AP214 and AP203 STEP files and translates them into 3D solids and surfaces.
Start IMPORT
Type IMPORT at the command line, or go to Insert tab → Import panel → Import.
Pick the STEP file
Set Files of type to STEP, select your .step or .stp file, and click Open.
Insert it when the import finishes
AutoCAD translates the file in the background and shows a notification bubble when it is done. Click the file name in the bubble to insert the model. If the bubble closed, right-click the import icon on the status bar and choose Insert.
Explode it to edit
The model arrives as a block. Run EXPLODE on it to get the individual solids and surfaces you can edit.
Which STEP version you were sent rarely matters for opening it; the differences are explained in STEP AP203 vs AP214.
Why can’t AutoCAD LT or AutoCAD for Mac open a STEP file?
Because neither one imports STEP. AutoCAD LT is a 2D product with no STEP option in IMPORT, and AutoCAD for Mac imports only ACIS (.sat), DXB and PDF files. To look at the part, use a browser viewer. To work with it, ask the sender for a SAT file on a Mac, or for 2D DWG views in LT.
Working the other way round? If all you have is a 2D drawing and the job needs the 3D part, plot the drawing to PDF and Drawing to STEP turns it into a checked 3D STEP model in minutes, from $29.99, from a PDF, PNG or JPG.
How do I convert a STEP file to STL or 3MF?
Upload the STEP, view it, and export the format you need: STL to 3D print, or 3MF for a modern slicer. The exact solid is sampled into triangles at a resolution you choose, and you do not need to learn CAD to do it.
This is the easy direction. Going back from STL to STEP does not restore the real curves (the STL to STEP converter rebuilds flat faces, not exact curves). Full walkthroughs in converting STEP to STL and 3D CAD file conversion tools, and the format trade-offs in STL vs STEP.
Which option should I pick?
Just need to see it or send it on? Use the browser viewer. Need to change the geometry? Use CAD, or full AutoCAD on Windows. Need a printable file? Convert it — no CAD skills required.
Frequently asked questions
What program opens a .stp file?
The same programs that open .step, because they are the same format: any CAD program, any CAM program at a machine shop, and browser-based 3D viewers. Windows Photos and macOS Preview do not read STEP, which is why a double-click usually does nothing.
Why will my computer not open a STEP file?
Because no default application is registered for it. STEP is a CAD interchange format, not a consumer document format, so a fresh Windows or macOS install has nothing associated with the extension. A double-click doing nothing is not a sign the file is corrupt.
Is there a free STEP file opener?
Yes. A browser viewer is the fastest free option when you only need to look at the part. FreeCAD is the free desktop option when you need to edit it. Both read .step and .stp files.
Does AutoCAD open STEP files?
Full AutoCAD on Windows does, through the IMPORT command rather than Open. AutoCAD LT and AutoCAD for Mac cannot import STEP at all, so use a browser viewer to look at the part, or ask the sender for a format your version reads.
Can I open a STEP file on my phone?
Yes, in a browser viewer. Upload the file from your phone and it renders as a 3D model you can rotate and zoom with your fingers, with no app to install.
Where can I open my STEP file right now?
Drop a .step or .stp file into PartWork.ai and see it in 3D in seconds — then export it, or describe a change and let the AI build a new version.
See importing and exporting files.
Free to upload & view — sign up to download
Open the studio, upload your STEP file, and view it in 3D free. Sign up (free) to download or convert it; credits to generate a new part — 50 for $4.99 (~10¢ each).