Vickers Hardness Number Calculator

How to use the Vickers hardness number calculator

What this calculator does

This calculator turns two observations from a Vickers indentation test – the applied Force (F) and the Mean diagonal length (d) – into four connected quantities. The main result is the Vickers hardness number (HV), expressed numerically in kilogram-force per square millimetre. It also reports Surface area hardness (H) in MPa, the calculated Indentation surface area, the converted Applied load in kgf, and an Estimated tensile strength (σᵤ). The hardness calculation is a geometric identity for the standard 136° Vickers indenter. The tensile-strength result is only an empirical screening estimate; it does not determine alloy grade, heat treatment, fracture behaviour, or certified tensile properties.

When to use it

Use the calculator when checking a laboratory worksheet after measuring a Vickers impression, comparing repeated indentations made at different loads, converting a force recorded in newtons into the conventional HV form, or preparing a quick engineering estimate before a fuller material-characterisation review. For conformity work, follow the applicable test method and equipment-verification requirements rather than relying on calculation alone. The current ISO 6507-1 Vickers test method specifies the metallic-material procedure and states a diagonal-length scope of 0.020 mm to 1.400 mm.

How to calculate

1. The calculator opens with a complete demonstration: 50 N and 0.5 mm. Its results and a validated example Excel workbook are immediately available.
2. Replace Force (F) with the load applied by the tester. Choose N or kgf; changing the unit converts the current value rather than relabelling it.
3. Replace Mean diagonal length (d) with the arithmetic mean of the two measured indentation diagonals. Choose mm or µm; the value is converted automatically when the unit changes.
4. Read Vickers hardness number (HV) first, then use the supporting results and the Calculation details table to audit the conversion path.
5. Select Download Excel to create a fresh .xlsx workbook from the current validated values. Reset clears the demonstration data and results; Download Excel then remains disabled until both required observations are complete and valid again.

Input guide

Force (F) is required and accepts a positive decimal number with a dot as the decimal separator; correctly grouped thousands commas are also accepted. Select N for newtons or kgf for kilogram-force. A realistic example is 50 N. Increasing force while the measured diagonal stays unchanged increases HV in direct proportion. Do not enter a force unit inside the number field, use scientific notation, or type a decimal comma such as 1,5; ambiguous or unsupported formats are rejected visibly.

Force unit is required and controls how the entered force is interpreted. The conversion uses standard gravity, 9.80665 N per kgf. For example, 50 N becomes approximately 5.09858 kgf. Switching units preserves the physical load and therefore does not change the calculated hardness apart from display-level rounding.

Mean diagonal length (d) is required and must be positive. Enter the mean of both diagonals, not one diagonal selected because it looks cleaner. A realistic example is 0.5 mm. Because diagonal length is squared in the denominator, a smaller indentation gives a sharply higher hardness result, while a larger indentation gives a lower result. Optical resolution, surface preparation, edge proximity, and distorted impressions can dominate the uncertainty, especially for very small indents.

Diagonal unit is required and accepts mm or µm. One millimetre equals 1,000 micrometres, so the startup value 0.5 mm converts to 500 µm. Changing this selector preserves the same physical length. The UK National Physical Laboratory's overview of Vickers hardness testing describes the 136° diamond indenter and the measurement of the two residual diagonals.

Output guide

Vickers hardness number (HV) is the primary result. It equals the applied load in kgf divided by the sloping surface area of the indentation in mm². A higher value means greater resistance to the standardized plastic indentation under the stated conditions. Zero is not a valid result because both required inputs must be positive. HV is an indentation-hardness number and should not be treated as a universal pressure measurement or a guaranteed material identity.

Surface area hardness (H) converts the HV number to MPa by multiplying by standard gravity. It is driven by the same force and diagonal values and is an exact unit conversion of the calculated HV value. Indentation surface area is the geometric sloping area represented by the 136° pyramid; it rises with the square of the mean diagonal. Applied load is the current load converted to kgf, which makes the conventional HV equation auditable.

Estimated tensile strength (σᵤ) uses the rule of thumb HV ÷ 0.3 to report MPa. A higher hardness generally yields a higher estimate, but the relationship varies with alloy, microstructure, work hardening, and heat treatment. Treat it as an estimate, not an exact conversion. The four header pills repeat the current load, diagonal, HV, and tensile estimate for quick scanning. The Calculation details table shows each intermediate quantity, its equation, and its current value; the Excel workbook reproduces those same canonical numbers.

Worked example

With the startup values, F = 50 N and d = 0.5 mm. First convert the load: 50 ÷ 9.80665 = 5.09858 kgf. The indentation surface area is 0.5² ÷ [2 × sin(68°)] = 0.134817 mm². Dividing the load by that area gives 37.8186, displayed as 37.82 HV. Multiplying by 9.80665 gives 370.87 MPa surface area hardness. Dividing HV by 0.3 gives the displayed empirical tensile-strength estimate of 126.06 MPa. These numbers match the first-open results, table, and workbook checkpoints.

Learn more

Hardness results depend on more than arithmetic. Indenter geometry, force application, optical measurement, test-block calibration, and uncertainty all matter. NIST provides information on hardness standard reference materials used to check microhardness instruments, while ASTM's collection of indentation hardness testing standards identifies the relevant Vickers and microindentation methods.