# Vickers hardness testers Optical indentation hardness measurement: force selection, specimen preparation, diagonal reading and verification. Reviewed: 2026-11-01 Tags: inspection, hardness, metrology ## What the tester measures Vickers hardness uses the mean of two diagonals left by a square-based diamond pyramid with 136° between opposite faces. Retain the applied force. [ZwickRoell, Vickers test method](https://www.zwickroell.com/industries/metals/metals-standards/vickers-test-iso-6507/) **Original arithmetic example, not an acceptance specification:** assume a 500 gf test with diagonals of 49 and 51 µm. The mean is 50 µm, so: **HV = 1854.4 × 500 / 50² = 370.88**, approximately **371 HV 0.5**. The suffix identifies the force as 0.5 kgf; it is not an uncertainty statement. Record dwell separately with the result. If the same impression were read as a mean of 51 µm, the calculated value would be 356.48 HV, about 3.9% lower. Thus, a 1 µm change in this example materially changes the result. This calculation isolates diagonal-reading sensitivity; it does not estimate the complete test uncertainty or establish that the assumed impression is valid. Vickers is useful when a test must address a small region, such as a prepared weld section or a hardness traverse, as well as for larger impressions. Define the material region and purpose before choosing force: a bulk acceptance result and a measurement intended to isolate a particular microstructural feature answer different questions. Hardness is a method-defined response, so retain force, loading cycle and indenter information with the number. [Struers, hardness testing principles](https://www.struers.com/en/knowledge/hardness-testing) ## Calculation and an illustrative result Using force **F in gram-force** and mean diagonal **d in micrometres**: **HV = 1854.4 × F / d²**, where **d = (d₁ + d₂) / 2**. Do not substitute newtons into that version of the equation. A normal dwell is 10–15 seconds; the specified procedure controls the actual cycle. [Struers, Vickers method and calculation](https://www.struers.com/en/knowledge/hardness-testing/vickers) ## Force, impression size and specimen limits ISO 6507-1:2023, fifth edition published October 2023, covers metallic materials, including hardmetals, and specified inorganic coatings. Its stated diagonal range is **0.020–1.400 mm**. Smaller impressions lie outside that document's scope because optical measurement limitations and tip imperfections create large uncertainties. A tester offering a very small force therefore does not establish that every resulting impression supports a conforming ISO result. [ISO 6507-1:2023, scope](https://www.iso.org/standard/83898.html) The same standard excludes coatings thinner than **0.030 mm** for tests normal to the surface and **0.100 mm** for cross-section tests. These are method-scope limits, not promises that every thicker coating can be measured: coating smoothness and thickness must still permit accurate diagonal reading. Select a suitable alternative method when the required feature falls outside scope. [ISO 6507-1:2023](https://www.iso.org/standard/83898.html) Specimen thickness, spacing and edge distance must suit the method and material. Struers summarizes an ISO minimum thickness of 1.5 times the diagonal and minimum impression-centre spacing of 3 diagonals for steel/copper, versus 6 for lead/zinc/aluminium. Apply the governing standard's complete rules, including its treatment of differing impression sizes; do not turn one spacing factor into a universal traverse pitch. Support the specimen so it cannot move during loading. [Struers, Vickers specimen and spacing guidance](https://www.struers.com/en/knowledge/hardness-testing/vickers) ## Preparation and optical reading The surface needs sufficient preparation for all four corners to be resolved. ZwickRoell identifies grinding and polishing as important because Vickers evaluation is optical. A surface that looks clean to the eye can still be unsuitable for measuring a small impression. Establish the preparation route on representative specimens before relying on automated batches. [ZwickRoell, surface quality and optical evaluation](https://www.zwickroell.com/industries/metals/metals-standards/vickers-test-iso-6507/) Control focus, illumination and contrast. Struers warns that these settings affect reproducibility and that dirty surfaces can mislead automatic impression recognition. Inspect stored images and corner placement, particularly when results change abruptly or the surface contains scratches and multiple phases. Repeating a software calculation cannot correct the wrong corners. [Struers, hardness testing and troubleshooting](https://www.struers.com/en/knowledge/hardness-testing) For a traverse, preserve coordinates and a specimen image so another reader can identify where each value came from. Investigate an unusually asymmetric, poorly resolved or interrupted impression against the selected procedure; avoid silently deleting inconvenient results or averaging them into apparently stable data. ## Instrument selection and verification As a bounded equipment example, Buehler's **Wilson VH3100/VH3300 brochure** lists 0.050–10 kgf for the VH3100 and 0.010–50 kgf for the VH3300, the latter depending on configuration. It lists different load cells, objectives and stage options. Confirm the installed configuration rather than treating the family maximum as the capability of every machine. The brochure carries copyright 2018 and document code FN01508_Wilson_VH3300_7-18; reconfirm its historical specifications for procurement. [Buehler brochure, printed pp. 20–23](https://www.buehler.com/assets/Brochures/English/Hardness/Wilson_VH3300_low.pdf) Camera magnification, stage positioning resolution and force accuracy describe different parts of the system. None alone is the uncertainty of the reported hardness. Qualify the complete measurement route at the intended force, impression size and specimen condition. Reference blocks support indirect checks of the complete tester. ZwickRoell supplies Vickers blocks by force and nominal hardness, with calibration certificates, and describes their use for indirect calibration and routine inspection. Choose blocks appropriate to the working scales and hardness range; retain their certificates and check results. A successful block check does not validate specimen preparation or every automatic reading. [ZwickRoell, hardness reference blocks](https://www.zwickroell.com/products/hardness-testing-machines/hardness-reference-blocks/) NIST identifies traceability and uncertainty reduction as central to hardness standardization and notes that corresponding ISO and ASTM requirements can differ. Specify the governing method and edition rather than combining convenient provisions from both. [NIST, updated March 26, 2025](https://www.nist.gov/programs-projects/hardness-standardization-and-measurements) ## Information to retain A useful result record includes specimen identity, section and test locations, method/edition, force and dwell, both diagonals, calculated HV values, preparation route, instrument configuration and verification status. Preserve individual results before summarizing a traverse or batch. Add the uncertainty and decision rule required by the acceptance agreement. The drawing or applicable product specification establishes acceptable hardness; the tester's catalogue does not. ## Related reference [Inspection and quality documents](../../sourcing/documents/index.md)