Surface Roughness Conversion Chart Tables- Engineers Edge

Surface Roughness Conversion Chart Tables

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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
Ra micro-meters	Ra micro-inches	RMS	CLA (N)	Rt	N	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.