# Open STEP Surface: Area Available, Volume Unavailable

Use a known planar STEP face to distinguish measurable surface area from unavailable solid volume.

This is one planar face, not a closed solid. A 20 × 30 mm face has 600 mm² area. Its enclosed solid volume is unavailable; zero would misrepresent the result.

[Open the matching tool](https://www.cadprops.com/tools/cad-surface-area/index.md) and [download open-surface.step](https://www.cadprops.com/samples/open-surface.step).

## Reproduce the check

1. Download the unchanged public sample. It is synthetic geometry generated in the repository, not a customer model.
2. Open it in CADProps and wait for the model canvas.
3. Open Properties, confirm units, included components and warnings.
4. Compare the displayed values with the analytical expectations below.
5. Open Files → Export CSV · mm / g, then reopen the downloaded properties CSV. Keep unavailable cells separate from zero.

## Expected and observed results

| Property | Analytical expectation | Observed CSV |
|---|---|---|
| X (mm) | 20 | 20 |
| Y (mm) | 30 | 30 |
| A (mm²) | 600 | 600 |
| V (mm³) | Unavailable (empty CSV cell) | Unavailable (empty CSV cell) |

The observed values and original CSV are recorded in the [verification record](https://www.cadprops.com/assets/evidence/seo-2026-10-01/cases.json). This record identifies the test environment and source revision. It describes a local verification run, not a production release.

<figure class="workflow-evidence"><img src="/assets/evidence/seo-2026-10-01/step-open-surface-volume-case-1440.webp" srcset="/assets/evidence/seo-2026-10-01/step-open-surface-volume-case-720.webp 720w, /assets/evidence/seo-2026-10-01/step-open-surface-volume-case-1440.webp 1440w" sizes="(max-width: 760px) 100vw, 920px" width="1440" height="1000" loading="lazy" alt="CADProps properties for the public open-surface.step sample"><figcaption>CADProps local verification; the screenshot shows the actual English interface.</figcaption></figure>

[Download the observed CSV](https://www.cadprops.com/assets/evidence/seo-2026-10-01/step-open-surface-volume-case.csv).

## Verification scope

Sample SHA-256: `3b9cfe6e949f4ab6b11716cc6d566a908d2077acfcfa5bc08fba18e5a677029c`. Generated by `scripts/make_samples.py`; source revision `27af64443aab95059aefa76ad27cefd267ebfbc4`. Verified on 2026-10-01 with the local isolated CADProps server and Chromium; see the linked record for environment details. Numerical comparison allows 0.01 mm for extents, 0.1 mm² for area and 0.1 mm³ for volume of these simple fixtures; these are test checks, not manufacturing tolerances.

CADProps processes files on the server. Inspect source units and warnings before relying on properties. Missing components describe only loaded scope; volume requires valid closed geometry. Ordinary assembly totals sum occurrences and can double-count overlapping material; they do not compute a Boolean union. Mass requires a density you confirm. [Accuracy](https://www.cadprops.com/accuracy/index.md) and [privacy](https://www.cadprops.com/privacy/index.md) explain the limits.

[Try the check](https://www.cadprops.com/tools/cad-surface-area/index.md) or [follow the measurement workflow](https://www.cadprops.com/workflows/measure-cad-properties/index.md).

## Related reading

- [STEP File Scale Wrong by 25.4? Fix Inch and mm Units](https://www.cadprops.com/guides/cad-model-wrong-scale-25-4/index.md)
- [How to Calculate Volume from a STEP File](https://www.cadprops.com/guides/calculate-step-volume/index.md)
- [Measure STEP Files Online: Dimensions, Distances & Units](https://www.cadprops.com/guides/measure-step-file/index.md)
- [Calculate Surface Area from a STEP File](https://www.cadprops.com/guides/surface-area-from-cad-file/index.md)
- [STEP File Volume Zero or Missing? Check Solid Geometry](https://www.cadprops.com/guides/why-step-volume-is-zero/index.md)

Original article: https://www.cadprops.com/guides/step-open-surface-volume-case/

HTML page: https://www.cadprops.com/guides/step-open-surface-volume-case/