Free STEP and STP file viewer for Android and Windows
PartLens opens .step and .stp files for free on Android and Windows, offline, with no login and no upload. It keeps the assembly tree, colours and units, measures holes and faces from the real geometry, and cuts sections through it.
STEP (ISO 10303, files ending .step or .stp) is the format almost every CAD system exports when a part has to travel: CATIA, NX, SolidWorks, Creo, Inventor and Fusion all write it. It carries the exact surfaces and edges of the part, not a picture of them, which is why it is the best file to ask a customer for.
What PartLens does with a STEP file
- Opens parts and assemblies — repeated parts are drawn once, so a die with hundreds of bolts still orbits smoothly on a phone.
- Measures from the real geometry — tap a bore for its diameter, a face for its area, two points for a distance. Every result says whether it is exact or approximate, and why.
- Charts holes and slots with shop-language callouts: counterbores, through and blind holes, pitch.
- Cuts sections with a live 2D profile you can measure and export as DXF.
- Isolates, hides and compares — one part of the assembly, or two revisions side by side.
- Reads the file's units (millimetres or inches) instead of guessing.
Open a STEP file
- Get PartLens free from Google Play or as a Windows download.
- On Android: Tap the file in WhatsApp, Gmail, Drive or your file manager and choose PartLens under Open with, or open PartLens and tap Open.
- On Windows: Install the free Windows app, then double-click the file, drag it onto the window, or use Open CAD….
Nothing is uploaded: the file is read on your device, with no account.
.step or .stp?
They are the same format. Both extensions hold the identical ISO 10303-21 text, and PartLens opens either. If a file opens as text starting with ISO-10303-21; it is STEP whatever its name says.
Very large assemblies
Phones get a mesh sized to their memory, and the model appears while it is still loading. For production assemblies of hundreds of megabytes, the free PartLens Converter prepares the file once on a PC into a .partlens package that opens almost at once on the phone.
Frequently asked questions
Is there a free STEP viewer for Android?
Yes. PartLens opens STEP and STP files on Android for free, with no ads, account or subscription, and works offline. Measurement and section views are included.
What is the difference between a STEP and an STP file?
There is none. .step and .stp are two extensions for the same ISO 10303-21 format, and PartLens opens both.
Can I measure a STEP file without CAD software?
Yes. PartLens measures diameters, distances, angles, face areas and hole positions straight from the STEP geometry and shows whether each number is exact or approximate.
Does PartLens upload my STEP files?
No. Files are read on your phone or PC and never uploaded. The only automatic request checks a small public version file for updates.
Can PartLens open STEP files on Windows?
Yes. PartLens for Windows is a free download that opens STEP and STP files with a searchable parts tree, measurement, exact sections, drafting and revision compare.
Open your file now, free
Free and offline on Android and Windows. No account, no upload.
Get it on Google Play Download for Windows