Machining

Surface Finish Converter

Convert between Ra, Rz, RMS, and other surface roughness scales.

Input Parameters

Units:

Mode

Surface Roughness Value

μin

Roughness Type

Results

Enter a roughness value to convert

What is Surface Finish?

Surface finish (roughness) measures the fine irregularities on a machined surface. It affects friction, wear, sealing ability, appearance, and fatigue life of parts.

This converter helps translate between different roughness parameters (Ra, Rz, RMS) and standards (N-grades, ISO) used worldwide.

How to Use

Select Convert mode to convert a roughness value
Or select Lookup mode to find values for an N-grade
Enter your roughness value and select the parameter type
Click Convert or Look Up to see all equivalent values
View typical machining methods for that finish

FAQs

Ra (Roughness Average) is the arithmetic mean of deviations from the mean line - most commonly specified. Rz is the average height difference between the five highest peaks and five lowest valleys. RMS (Root Mean Square) is similar to Ra but squares values before averaging, making it about 11% higher than Ra.

1 μm = 40 μin (approximately 39.37). So 1.6 μm = 64 μin, 3.2 μm = 125 μin. Imperial (microinches) is common in the US; metric (micrometers) is standard elsewhere. Both measure the same thing - just different units.

Match finish to function: sealing surfaces need 32-63 μin (0.8-1.6 μm), general machined surfaces 125-250 μin (3.2-6.3 μm), bearing surfaces 8-32 μin (0.2-0.8 μm). Tighter tolerances cost more - don't over-specify.

Each process has a typical finish range: grinding 8-32 μin, turning/milling 32-250 μin, sawing 500-2000 μin. Better finishes require slower feeds, sharper tools, or secondary operations like grinding or honing.

N-grades (N1-N12) are ISO roughness grades where each number is roughly double the previous Ra value. N1 is the smoothest (1 μin), N12 is roughest (2000 μin). Most machined parts fall in N6-N9 range.

Limitations

• Ra to Rz conversion is approximate (ratio varies by profile)
• Machining methods shown are typical - actual results vary
• Does not include waviness, lay direction, or other parameters
• Actual measurement depends on stylus and cutoff settings
• For critical applications, specify exact parameter and method