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Parameter Name
Ra Roughness Average (Ra)
Rq Root Mean Square (RMS) Roughness
Rt Maximum Height of the Profile
Rv, Rm Maximum Profile Valley Depth
Rp Maximum Profile Peak Height
Rpm Average Maximum Profile Peak Height
Rz Average Maximum Height of the Profile
Rmax Maximum Roughness Depth
Rc Mean Height of Profile Irregularities
Rz(iso) Roughness Height
Ry Maximum Height of the Profile
Wt, W Waviness Height
S Mean Spacing of Local Peaks of the Profile
Sm, RSm Mean Spacing of Profile Irregularities
D Profile Peak Density
Pc Peak Count (Peak Density)
HSC Hight Spot Count
la Average Wavelength of the Profile
lq Root Mean Square (RMS) Wavelength of the Profile
Da Average Absolute Slope
Dq Root Mean Square (RMS) Slope
Lo Developed Profile Length
lr Profile Length Ratio
Rsk,Sk Skewness

Surface Finish Definitions:

  1. Ra: Ra is the arithmetic average of the absolute values of the roughness profile ordinates. Also known as Arithmetic Average (AA), Center Line Average (CLA). The average roughness is the area between the roughness profile and its mean line, or the integral of the absolute value of the roughness profile height over the evaluation length
  2. Rz: Rz is the arithmetic mean value of the single roughness depths of consecutive sampling lengths. Z is the sum of the height of the highest peaks and the lowest valley depth within a sampling length.
  3. Cutoff λc: of a profile filter determines which wavelengths belong to roughness and which ones to waviness.
  4. Sampling Length: is the reference for roughness evaluation. Its length is equal to the cutoff wavelength.
  5. Traversing Length: is the overall length traveled by the stylus when acquiring the traced profile. It is the total of Pre-travel, evaluation length and post travel
  6. Evaluation Length: is the part of the traversing length from where the values of the surface parameters are determined.
  7. Pre-Travel: the first part of the traversing length.
  8. Post-Travel: The last part of the traversing length

Selection of Cutoff λc

Profile Cutoff Sampling/Evaluation Length
Rz (μm) Ra (μm) λc (mm) lr / ln (mm)
Up to .1 Up to .02 .08 .08 / .4
Over .1
up to .5
Over .02
up to .1
.25 .25 / 1.25
Over .5
up to 10
Over .1 up top 2 .8 .8 / 4
Over 10
up to 50
Over 2 up to 10 2.5 2.5 / 12.5
Over 50
up to 200
Over 10 up to 80 8 8 / 40


Surface Roughness Measurement Guide NIST Links
Surface Roughness Profile Parameters ASTM Links