Surface Roughness Converter
Convert surface roughness values between micrometers and microinches, and estimate common Ra, Rq and Rz relationships for CNC machined surfaces.
Ra, Rq & Rz Roughness Converter
Enter a roughness value and select the parameter and unit.
Unit conversion between µm and µin is exact within normal rounding. Ra, Rq and Rz are different surface parameters and cannot be universally converted with a fixed ratio. Rq and Rz values shown here are approximate engineering estimates only.
Surface Roughness Reference Chart
The table below shows common Ra values used on CNC machining drawings. The finish descriptions are general references only because actual surface appearance depends on the machining process, material, tooling and direction of the surface pattern.
| Ra (µm) | Ra (µin) | General Finish Description |
|---|---|---|
| 12.5 | 492 | Rough machined surface |
| 6.3 | 248 | General rough machining |
| 3.2 | 126 | Standard machined finish |
| 1.6 | 63 | Fine machined finish |
| 0.8 | 31.5 | Fine precision finish |
| 0.4 | 15.7 | Very fine finish / grinding range |
| 0.2 | 7.9 | Precision grinding / finishing |
| 0.1 | 3.9 | Very fine lapped or polished finish |
Arithmetic Average Roughness
Ra is the arithmetic average of the absolute profile deviations from the mean line and is one of the most commonly specified roughness parameters on engineering drawings.
Root Mean Square Roughness
Rq is the root mean square of the profile deviations. It gives more weight to larger peaks and valleys than Ra.
Maximum Height of Profile
Rz evaluates peak-to-valley height and is more sensitive than Ra to larger surface peaks, valleys and individual profile features.
Surface Roughness FAQ
What does Ra 1.6 mean?
Ra 1.6 means an arithmetic average surface roughness of 1.6 µm, which is approximately 63 microinches.
What is Ra 3.2 in microinches?
Ra 3.2 µm is approximately 126 µin.
Is Ra the same as Rz?
No. Ra represents average roughness, while Rz evaluates peak-to-valley height. They describe different characteristics of the surface profile.
Can Ra and Rz be converted exactly?
No. Their relationship depends on the actual surface profile and manufacturing process. Any Ra-to-Rz conversion should be treated as an approximate estimate unless both values have been measured.
What surface roughness is common for CNC machining?
Ra 3.2 µm and Ra 1.6 µm are commonly encountered machining requirements. Finer finishes may be achievable with suitable tooling, machining parameters and additional finishing operations.
Need a Specific Surface Finish on Your CNC Parts?
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