Surface Finish Converter

Enter a value in any field to see the conversion across other measurement systems.

Ra - Metric ($\mu m$)

$\mu m$

Ra - Imperial ($\mu in$)

$\mu in$

Rz - Metric ($\mu m$)

$\mu m$

Estimated as $Ra \times 4$

RMS / Rq ($\mu in$)

$\mu in$

Estimated as $Ra \times 1.11$

ISO Roughness Grade (N-Number)

N --

Ra (Arithmetic Average): The most common parameter. It is the average absolute distance from the mean line to the profile.

Rz (Mean Peak-to-Valley): The average of the highest peaks and lowest valleys. In the US, this is often estimated as $4 \times Ra$.

RMS (Root Mean Square): Similar to Ra but uses the geometric average. Generally $1.11 \times$ higher than Ra.

ISO Grade	Ra ($\mu m$)	Ra ($\mu in$)	Process Example
N10	12.5	500	Rough Turn
N8	3.2	125	Standard Mill
N7	1.6	63	Finish Mill
N6	0.8	32	Grinding
N4	0.2	8	Polishing

Note: Conversions between Ra and Rz are approximations. The actual ratio depends on the manufacturing process (turning vs. grinding).