Surface Roughness Conversion Chart Tables

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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
35.6
32
4.0
6
0.03
0.8
1.6
63
69.3
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
Rt = R a x 8.7
Rz = R a x 7.2
Rz ISO = R a x 7.6
Rmax = R a x 8.0
Rp = R a x 3.6
RPM = R a x 2.9
RMS = R a x 1.1

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

Surface Roughness Value Equivalents

The 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.

  • ASME B46.1
  • ASME Y14.36M - 1996 Surface Texture Symbols
  • ISO 468:1982 “Surface roughness — parameters. Their values and general rules for specifying requirements.”
  • ISO 4287:1997 “Surface texture: Profile method — Terms, definitions and surface texture parameters.”
  • ISO 4288:1996 “Surface texture: Profile method — Rules and procedures for the assessment of surface texture.” Includes specifications for precision reference specimens, and roughness comparison specimens, and establishes requirements for stylus-type instruments.”
  • ISO 8785:1998 “Surface imperfections — Terms, definitions and parameters.”
  • ISO 10135-1:CD “Representation of parts produced by shaping processes — Part 1: Molded parts.”

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