SolidWorks calculates the weight of a 3D part through its built-in Mass Properties tool, which multiplies the part's geometric volume by its assigned material density and reports the result in grams, kilograms, or pounds. The whole calculation rests on one equation from physics: Weight = Volume × Density. SolidWorks needs two things to return a non-zero number — a closed, watertight body so the volume is well-defined, and a material whose density the database knows. The moment a material is assigned from the library, the Evaluate tab's Mass Properties command refreshes the readout instantly. If your alloy isn't in the library — a niche stainless grade, a specific aluminum temper, an exotic brass — you can still get a valid answer by editing the material and typing the density in yourself. Below are the step-by-step instructions inside SolidWorks, the underlying geometry that drives the volume term, and a fast path for raw stock bar, pipe, sheet, or hex bar when you don't have a CAD model in front of you.
Use the SolidWorks Mass Properties Tool
SolidWorks treats weight as a live property of the part file, so the answer stays correct whenever the geometry changes. The tool lives on the Evaluate tab and depends entirely on whether the active document has a material assigned. If the FeatureManager design tree on the left shows a plain Material entry rather than a named alloy, the mass will be reported as zero regardless of how complex the part is.
- Open the part (.sldprt) or assembly (.sldasm) you want to weigh in SolidWorks.
- In the FeatureManager design tree on the left, right-click Material and select Edit Material. Pick the closest match from the SolidWorks material library — steel, aluminum 6061, brass C360, ABS, etc. — and click Apply, then Close.
- Click the Evaluate tab on the CommandManager ribbon at the top of the screen.
- Click the Mass Properties icon (the blue scale symbol). SolidWorks opens the Mass Properties dialog.
- Read the mass value at the top of the dialog. Below it you will see the projected surface area, volume, density used, and center of mass coordinates.
- To switch units (grams ↔ kilograms ↔ pounds), click Options at the bottom of the dialog or use Tools → Options → Document Properties → Units before running the command.
- To keep a record, click Print inside the Mass Properties dialog — it exports the table including density and volume to a printer, file, or clipboard.
The value SolidWorks reports is mass (kilograms or pounds), not force (newtons or pound-force). For almost every engineering and quoting task the distinction doesn't matter, but in physics, weight is the force due to gravity — W = m · g — so to convert the displayed mass to force in newtons, multiply by 9.81 m/s².
Override the Density for Custom Materials
If the exact alloy you need isn't in the SolidWorks library — and the library is large but not exhaustive — you can still get an accurate weight by typing the density in yourself. This is the right path for work-hardened tempers, niche stainless grades, custom polymers, or any metal whose published density you trust more than the library's generic value.
- Right-click Material in the design tree and choose Edit Material.
- In the material tree, expand a category close to your alloy and click any item.
- In the Properties panel on the right, scroll to Density and select Custom from the units dropdown.
- Type the density value in kg/m³ (or g/cm³ — 1 g/cm³ equals 1,000 kg/m³) and click Apply.
- Run Evaluate → Mass Properties. The reported mass will now use your override instead of the library default.
For metals that don't appear in the density table below, the mill test certificate is the most authoritative source — it lists the measured density for the exact heat you received, accounting for composition and processing.
The Formula Behind SolidWorks's Number
What SolidWorks actually does — and what any metal weight calculator ultimately does — is multiply the geometric volume of the part by the density of the material. The cross-section of the part gets computed in CAD space; the density comes from the material assignment. The whole calculation collapses to:
Weight = Volume × Density
That's the entire physics. The rest is geometry: how to compute the volume of a specific shape so the multiplication gives a useful number. For most engineering work, the densities that matter are these typical values:
| Metal | Density (kg/m³) | Density (g/cm³) | Notes |
|---|---|---|---|
| Steel (carbon) | 7,850 | 7.85 | Most common structural steel |
| Stainless steel (304) | 8,000 | 8.00 | Austenitic grade — common reference |
| Aluminum | 2,700 | 2.70 | Generic 6000-series value |
| Copper | 8,960 | 8.96 | Pure copper, C110 |
| Brass | 8,500 | 8.50 | Typical yellow brass C360 |
| Titanium | 4,500 | 4.50 | Commercially pure grade |
These are typical engineering values — accurate to within roughly 1–2 percent for estimating, but the exact alloy, temper, and cold-work history can shift the true density by a similar margin. For a final quote or a safety-critical calculation, the mill certificate's measured density is the final word.
Estimate Stock Weight Without a CAD Model
Most of the time you can simply open the part in SolidWorks and let Mass Properties do the work. But for quick checks — quoting a customer's bar length, weighing raw stock before cutting, pricing scrap, or sizing a shipment — you often only have the dimensions of the stock itself: a 6 m length of 50 mm OD pipe, a 1220 × 2440 mm sheet of 3 mm steel, a 24 mm hex bar. CAD isn't needed for that. The same Weight = Volume × Density equation runs entirely on shape formulas, and a browser-based Metal Weight Calculator applies the right one for each profile. It covers round bar, square bar, round pipe/tube, rectangular sheet, and hexagon bar across six common metals — steel, stainless 304, aluminum, copper, brass, titanium — in metric (mm → kg) or imperial (in → lb). Pick the profile, pick the metal, type the dimensions, and the weight appears instantly alongside the cross-section area, volume, and density used. Everything runs locally in the browser, so proprietary dimensions never leave your device.
Worked example — a steel pipe with 50 mm outer diameter, 5 mm wall thickness, 1000 mm length comes out to about 5.55 kg:
Outer radius R = 50 / 2 = 25 mm = 0.025 m Inner radius r = R − wall = 25 − 5 = 20 mm = 0.020 m Cross-section area = π · (R² − r²) = π · (0.025² − 0.020²) = π · (0.000625 − 0.000400) = π · 0.000225 ≈ 0.000707 m² Volume = 0.000707 × 1 m = 0.000707 m³ Weight = 0.000707 × 7,850 kg/m³ ≈ 5.55 kg
The same math holds in imperial — enter the inches, read the pounds.
Cross-Section Formulas by Profile
Each profile has a closed-form geometry — no integration, no approximation. The calculator picks the right one automatically:
| Profile | Dimensions required | Cross-section area |
|---|---|---|
| Round bar | Diameter, length | π · r² |
| Square bar | Side, length | s² |
| Round tube / pipe | OD, wall thickness, length | π · (R² − r²) |
| Rectangular sheet / plate | Length, width, thickness | W × T |
| Hexagon bar | Across-flats (A/F), length | (√3 / 2) · F² |
Two subtleties worth flagging. For pipe, wall thickness is subtracted twice — once from the outer radius on each side — so a 50 mm OD × 5 mm wall pipe has an inner diameter of 40 mm, not 45 mm. For hex bar, the dimension the calculator asks for is the distance across flats (the wrench size that hex stock is actually sold by), not corner-to-corner and not the side length. A 24 mm A/F hex bar has a cross-section of about 499 mm² — using s² instead would give 576 mm², an error of more than 15 percent.
Why the Calculated Weight Can Differ From a Real Weigh-In
Two predictable sources explain any gap between the figure SolidWorks (or the calculator) returns and the weight on a real scale.
Material density is quoted for a typical alloy. AISI 304 stainless, for instance, sits in a band from about 7,900 to 8,030 kg/m³ depending on the exact chromium and nickel content and any cold work. The library value of 8,000 kg/m³ puts you within roughly 1 percent of the real number for most 304 bar and plate, but for a custom heat or a heavily work-hardened temper the offset grows.
Real parts carry mill tolerances. A nominal 50 mm OD pipe can legally measure between about 49.05 and 50.95 mm depending on the schedule and the standard. A 5 mm wall can be 4.05 to 5.95 mm. Both tolerances shift the cross-section area — and therefore the weight — by a few percent in either direction. Sheet metal thickness has its own published plus/minus ranges. None of them change the formula, but they all widen the band between the calculated weight and the scale.
For quoting, material take-off, and shipping estimates, these tolerances are well within the noise floor of the decision, which is why SolidWorks's Mass Properties — and a free calculator using the same physics — are the right tools. For a buy-to-fly analysis on a flight-critical aerospace part or a structural certification, weigh the finished part or pull the number from the mill certificate.