Ra to Rz Converter
Convert Ra surface roughness values to estimated Rz values in micrometers or microinches.
This tool provides an estimated Ra to Rz conversion based on common engineering roughness ratios. Ra and Rz cannot be converted exactly, so the result should be used as a reference only.
Enter a valid positive Ra value.
Ra and Rz cannot be converted exactly. This calculator provides estimated engineering reference values only. Actual results may vary depending on surface profile, material, machining process, cutoff length, and measurement method.
Ra to Rz Conversion Formula
The commonly used engineering estimate is Rz ≈ Ra × 5. For many machined surfaces, a broader reference range is Rz ≈ Ra × 4 to 7.
Ra to Rz Conversion Chart
| Ra (µm) | Est. Rz (µm) | Typ. min (µm) | Typ. max (µm) |
|---|---|---|---|
| 0.1 | 0.5 | 0.4 | 0.7 |
| 0.2 | 1 | 0.8 | 1.4 |
| 0.4 | 2 | 1.6 | 2.8 |
| 0.8 | 4 | 3.2 | 5.6 |
| 1.6 | 8 | 6.4 | 11.2 |
| 3.2 | 16 | 12.8 | 22.4 |
| 6.3 | 31.5 | 25.2 | 44.1 |
| 12.5 | 62.5 | 50 | 87.5 |
| 25 | 125 | 100 | 175 |
| 50 | 250 | 200 | 350 |
Est. Rz = Ra × 5 · Typical range = Ra × 4 to Ra × 7 (µm)
Why Ra to Rz Conversion Is Only an Estimate
Ra is an average roughness value, while Rz is based on peak-to-valley height. Because they describe different surface characteristics, there is no exact universal conversion between Ra and Rz.
FAQ
Can Ra be converted directly to Rz?▼
No. Ra and Rz describe different surface roughness characteristics. This calculator provides an estimated value only.
What is the common Ra to Rz formula?▼
A common engineering estimate is Rz ≈ Ra × 5. A broader reference range is Rz ≈ Ra × 4 to 7.
Is Rz always 5 times Ra?▼
No. The ratio depends on surface profile, machining process, material, cutoff length, and measurement method.
How do I convert Rz to Ra?▼
Use the Rz→Ra calculator or bidirectional mode. A common engineering estimate is Ra ≈ Rz ÷ 5, with a broader reference range of Ra ≈ Rz ÷ 7 to Rz ÷ 4. Results are approximate only.