Calculate part weight from a STEP or STP file
Open your CAD solid, choose a material, and TinyJig calculates its weight from the volume enclosed by its actual surfaces. STEP and STP are two extensions for the same file format. This tool works with sheet-metal parts, CNC-machined components, and other closed solid models. Holes, pockets, and internal cavities are included in the volume calculation. The empty space around a part is not material: a bounding box is useful for checking dimensions, but it would greatly overstate the weight of a bracket or enclosure.
The model is rendered in an interactive 3D view. Drag to orbit it and scroll to zoom, then check its overall dimensions before relying on the result. STEP units are converted to millimeters internally; the dimension selector changes the displayed measurements without resizing the model. Weight can be displayed in grams, kilograms, ounces, or pounds. Multiple closed solids are weighed together using one selected material. For an assembly made from several materials, export the relevant bodies separately and calculate each material group.
Compare aluminum, steel, plastics, and other materials
Start with a single selected material to keep the result easy to read. Open the comparison table when you want to see the same geometry in every available material. The table shows nominal density, calculated part weight, and the percentage difference from your selected material. Search by material name or group, sort by weight or name, and select a row to make it the active material. A CSV download records the compared weights, quantity, volume, geometry status, and density references.
The library covers the named material families in SendCutSend’s sheet catalog, along with separate mild-steel grade identities and 6061 CNC billet. It includes aluminum alloys, stainless and carbon steels, brass, copper, titanium, plastics, laminates, wood products, rubber, foam, and adhesive tape. Coverage does not mean that all materials can be bent or manufactured with the same processes. Nominal density is a physical property used for comparison; strength, corrosion resistance, temperature limits, and supplier stock need separate consideration.
Change sheet thickness by flattening and rebending
For supported sheet-metal solids, TinyJig recognizes a uniform wall thickness and the connected planar panels and cylindrical bends. It unfolds those panels into a flat outline and records the bend centerlines, angles, and inside radii. Changing thickness creates a new solid from that outline, then bends it again along the recovered lines. The weight comes from the rebuilt solid’s measured volume. This is an actual geometry change that you can inspect and download, rather than multiplying the old weight by a thickness ratio.
The flat outline and bend centerlines remain fixed while the new material thickness changes the bend allowance. Original inside bend radii and angles are retained. Finished flange dimensions can therefore change. Toggle between the original model, the updated part, and the flat pattern to inspect the result. Changing a material alone changes density and weight; it does not automatically resize the geometry or substitute a manufacturer’s tooling radius. Enter a thickness in millimeters or inches, use a preset, or type a fractional expression such as 1/16 in.
Understand the K-factor and bend allowance
A STEP file describes final surfaces but usually does not preserve the sheet-metal feature history or the K-factor used to develop its flat pattern. TinyJig begins with a K-factor of 0.42. You can change it in the bend details before applying a thickness change. The K-factor describes the neutral axis position as a fraction of thickness measured from the inside of a bend. Bend allowance is the absolute bend angle in radians multiplied by the sum of inside radius and K-factor times thickness.
Changing the K-factor recovers a different flat pattern from the original uploaded part. With that factor held fixed, later thickness revisions reuse its flat outline and centerlines. A recovered flat pattern is consequently conditional on the chosen factor; it is not proof of the original designer’s manufacturing rule. Use the appropriate factor for your material and process, check critical formed dimensions, and confirm tooling with the fabricator. TinyJig preserves the imported inside radii rather than automatically adopting SendCutSend or another supplier’s thickness-specific radii.
Download the updated model as a STEP solid
Apply a thickness change before downloading. TinyJig validates the rebuilt model, checks for overlapping formed pieces, and measures the resulting solid. The updated STEP download uses the same geometry as the current-part preview and weight calculation, with explicit millimeter units. A separate flat STEP download contains the recovered flat geometry extruded to the selected thickness. These exports preserve analytic panel edges and cylindrical bend surfaces rather than exporting the triangles used for display.
If a new thickness would consume a flange, cross a hole near a bend, or cause a collision, TinyJig reports the problem and retains the last valid model. Unapplied changes must be resolved before a download is enabled. After export, open the STEP in your receiving CAD system and inspect fit-critical features. A valid solid does not establish press-brake accessibility, a viable bend sequence, material formability, or a supplier’s willingness to manufacture the part.
Which models support thickness editing?
Weight calculation requires valid closed solids. Thickness editing additionally needs one connected sheet with a uniform thickness between 0.1 and 25 millimeters, planar flanges, and recognizable straight cylindrical bends. Up to 16 bends can be reconstructed, including finite-length tab bends and connected flanges on different axes. The recovered sheet is rebuilt at its original thickness and compared with the original solid before editing is enabled. This checks the reconstruction’s geometry rather than accepting a matching total volume alone.
Variable-wall CNC parts, open surfaces, chamfers that change sheet thickness, stamped features, curved bends, closed bend cycles, and some interacting or changing-width bend regions cannot currently be reconstructed. For these cases, the original model can still be weighed if it is a valid solid, and the interface explains why thickness editing is unavailable. Files are limited to 25 MB and 100 solid bodies for weight calculation. A processing timeout and cancel control keep a difficult import from occupying the page indefinitely.
How volume and density become weight
The calculation is mass = volume × density. With volume in cubic millimeters and density in kilograms per cubic meter, divide their product by one billion to obtain kilograms. For example, a 100 mm cube contains 1,000,000 cubic millimeters, or 0.001 cubic meters. At a custom density of 7,850 kg/m³, that cube weighs 7.85 kg. Removing holes reduces the measured volume and weight. Changing preview detail does not change the solid-volume calculation.
Physical weight remains an estimate because material density, stock thickness, and manufacturing tolerances vary. The density source is available beside each selection. Composite layups, wood moisture, rubber formulations, and foam grades need particular care. ACM uses an explicit aluminum-skin and polymer-core model that depends on sheet thickness; for other geometry it uses a 3 mm panel reference. Enter a custom density when you have data for your actual stock. Quantity multiplies part weight into batch weight, excluding packaging, added coatings, and unmodeled hardware.
Local CAD processing, without an account
Your selected STEP file is read and processed in your browser. TinyJig does not upload the file, its name, or its geometry to a conversion server. CAD work runs in a background worker, and downloads are generated on your device. The site can remember your selected material, but it does not save the uploaded CAD model. Reloading or leaving the page discards the working geometry. The sample bracket is a public example supplied with the application.
Anonymous usage events help improve file support and the calculator’s reliability. These events identify the page, file format, sample status, and import or export outcome rather than storing your design. Normal website requests still retrieve the application and geometry libraries. If you are starting from vector artwork, use TinyJig’s existing converter to make a STEP solid; if you need to design the blank and bends themselves, use the sheet-metal workspace. Return here to compare material weights and inspect supported thickness revisions.