#### Surface Roughness Conversion Chart Tables

Surface Roughness Review
Surface Roughness Standards Comparator

The following charts and tables convert surface finish or roughness between selected industry standard units.

Where:

Ra = Roughness, average in micro-meters & micro-inches
RMS = Root Mean Square in micro-inches
CLA = Center Line average in micro-inches
Rt = Roughness, total in microns
N = New ISO (Grade) Scale numbers
Cut-Off Length = Length required for sample.

Conversion math at bottom --

Surface Roughness Conversion Chart
Ra
micro-meters
Ra
micro-inches
RMS
CLA
(N)
Rt
N
Cut-Off Length
in.
mm
0.025
1
1.1
1
0.3
1
0.003
0.08
0.05
2
2.2
2
0.5
2
0.01
0.25
0.1
4
4.4
4
0.8
3
0.01
0.25
0.2
8
8.8
8
1.2
4
0.01
0.25
0.4
16
17.6
16
2.0
5
0.01
0.25
0.8
32
32.5
32
4.0
6
0.03
0.8
1.6
63
64.3
63
8.0
7
0.03
0.8
3.2
125
137.5
125
13
8
0.1
2.5
6.3
250
275
250
25
9
0.1
2.5
12.5
500
550
500
50
10
0.1
2.5
25.0
1000
1100
1000
100
11
0.3
8.0
50.0
2000
2200
2000
200
12
0.3
8.0

Conversions (math):

CLA (micro inches) = Multiply Ra(µm) x 40

RMS * (acceptable 1.1 - 1.7 factor) = Multiply CLA x 1.1

Parameter Conversion Formula

To convert a known Ra value to a different parameter, use the following formula:
Ra x Parameter Factor = Desired Parameter

Example:

Ra to Rt:
1.0 micrometer Ra x 8.7 (Rt Factor) = 8.7 micrometer Rt
40 microinch Ra x 8.7 (Rt Factor) = 348 microinch Rt

 Parameter Factor Rt 8.7 Rz 7.2 Rz ISO 7.6 Rmax 8.0 Rp 3.6 RPM 2.9 RMS 1.1

Surface Roughness Value Equivalents

Thye Waviness is the measure of surface irregularities with a spacing greater than that of surface roughness. These usually occur due to warping , vibrations , or deflection during machining.