Rz to Ra Converter
Convert Rz surface roughness values to estimated Ra values in micrometers or microinches.
Use this Rz to Ra converter to estimate Ra values from Rz surface roughness measurements. The result is based on common engineering conversion ratios and should be used as a reference only.
Enter a valid positive Rz value.
Rz and Ra cannot be converted exactly. This calculator provides estimated engineering reference values only.
Rz to Ra Conversion Formula
The commonly used engineering estimate is Ra ≈ Rz ÷ 5. A broader reference range is Ra ≈ Rz ÷ 7 to Rz ÷ 4.
Rz to Ra Conversion Chart
| Rz (µm) | Est. Ra (µm) | Typ. min (µm) | Typ. max (µm) |
|---|---|---|---|
| 0.1 | 0.02 | 0.014 | 0.025 |
| 0.2 | 0.04 | 0.029 | 0.05 |
| 0.4 | 0.08 | 0.057 | 0.1 |
| 0.8 | 0.16 | 0.114 | 0.2 |
| 1.6 | 0.32 | 0.229 | 0.4 |
| 3.2 | 0.64 | 0.457 | 0.8 |
| 6.3 | 1.26 | 0.9 | 1.575 |
| 12.5 | 2.5 | 1.786 | 3.125 |
| 25 | 5 | 3.571 | 6.25 |
| 50 | 10 | 7.143 | 12.5 |
Est. Ra = Rz ÷ 5 · Typical range = Rz ÷ 7 to Rz ÷ 4 (µm)
Why Rz to Ra Conversion Is Only an Estimate
Rz is based on peak-to-valley height, while Ra describes average roughness. Because they measure different surface characteristics, there is no exact universal conversion between Rz and Ra.
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.