Free Engineering Tool
Surface Parameters Calculator — ISO 21920
Enter Ra value or measurement data to see estimated Rz, Rq, Rt relationships and recommended filter cutoff per ISO 21920.
Estimated Parameters
Profile Parameters
| Parameter | Definition | Approx. Relation to Ra |
|---|---|---|
| Ra | Arithmetical mean of |Z(x)| over evaluation length | 1.0 × Ra |
| Rq | Root mean square of Z(x) | 1.11 × Ra (Gaussian) |
| Rz | Max height: average of 5 highest peaks + 5 deepest valleys | 4–7 × Ra (process dependent) |
| Rt | Total height: max peak to min valley over full length | 5–10 × Ra |
Default Filter Cutoff (λc)
| Ra Range (μm) | λc (mm) | Evaluation Length (mm) |
|---|---|---|
| 0.006 – 0.02 | 0.08 | 0.4 |
| 0.02 – 0.1 | 0.25 | 1.25 |
| 0.1 – 2.0 | 0.8 | 4.0 |
| 2.0 – 10 | 2.5 | 12.5 |
| 10 – 80 | 8.0 | 40.0 |
Note: The Ra-to-Rz conversion is approximate and depends heavily on the machining process. Always measure directly when possible.
Professional instruments.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
