Vickers Hardness Number Calculator

The Vickers hardness test uses a square-based diamond pyramid indenter with an apex angle of 136 degrees between opposite faces. The core formula to determine the Vickers Hardness Number (HV) is:

HV = (2 * F * sin(θ / 2)) / (g * d²)

Where F is the applied force in Newtons, θ is the indenter angle (typically 136°), g is standard gravity, and d represents the mean diagonal length of the indentation (calculated as the average of diagonal1 and diagonal2). Once HV is established, additional material characteristics can be derived: hardness in standard engineering units via 9.80665 * HV, and approximate ultimate tensile strength using the conversion factor HV / 0.3 for specific alloy categories.

Imagine you perform a materials test on a specialized steel alloy using a testing machine. You apply an indentation force (F) of 98.07 Newtons. Under a microscope, you measure the two diagonals of the resulting square indentation: diagonal 1 is 0.201 mm and diagonal 2 is 0.203 mm. First, find the diagonal mean: d = (0.201 + 0.203) / 2 = 0.202 mm. Next, apply the standard 136-degree pyramid angle where sin(68°) equals approximately 0.9272. Substituting these figures into the formula gives HV = (2 * 98.07 * 0.9272) / (9.80665 * 0.202²), which results in a Vickers Hardness Number of approximately 220 HV. Using this result, the estimated tensile strength would be roughly 220 / 0.3, yielding approximately 733 MPa.

To ensure maximum precision when utilizing this calculator, always measure your indentation diagonals under high magnification using a calibrated optical eyepiece. Ensure that the test specimen has a smooth, flat, and polished surface; surface roughness can distort the boundary edges of the diamond impression and skew your diagonal readings. Additionally, make sure your applied load and dwell time comply with ISO or ASTM testing standards for the specific material category you are evaluating.