Ra Surface Roughness Input Form
Enter measured profile heights from a stylus, lab sheet, or inspection export. The page uses a responsive three-column input layout on large screens, two columns on medium screens, and one column on mobile.
Example Data Table
| Point | Position | Height | Unit |
|---|---|---|---|
| 1 | 0.0 | 2.5 | µm |
| 2 | 0.8 | -1.2 | µm |
| 3 | 1.6 | 1.8 | µm |
| 4 | 2.4 | -2.1 | µm |
| 5 | 3.2 | 0.9 | µm |
| 6 | 4.0 | -0.7 | µm |
| 7 | 4.8 | 1.4 | µm |
| 8 | 5.6 | -1.8 | µm |
Formula Used
Ra = (1 / L) × ∫ | y(x) | dx
Ra = (|y₁| + |y₂| + ... + |yₙ|) / n
yᵢ = centered profile height at point i after subtracting the mean line.
n = number of measured points.
L = evaluation length.
This calculator first finds the mean line, centers the profile, converts each deviation to its absolute value, and then averages those absolute deviations to produce Ra.
How to Use This Calculator
- Enter a part name, batch number, and inspection source.
- Paste measured profile heights into the values field.
- Set point spacing, unit, evaluation length, and cut-off length.
- Select the filter label matching your process or report.
- Click Calculate Ra Surface to generate the result.
- Review Ra, Rq, Rt, plotted profile, and the computed table.
- Use the CSV or PDF buttons to export the result.
What Is an Ra Surface Value?
Ra is the arithmetic average roughness of a measured surface profile relative to its mean line. In engineering, it helps compare finish quality across turning, grinding, milling, polishing, coating preparation, sealing faces, bearing seats, and precision contact surfaces.
Frequently Asked Questions
What is Ra in surface roughness?
Ra is the arithmetic average of absolute profile deviations from the mean line over the evaluation length. It is one of the most used roughness indicators for machined and finished surfaces.
How is Ra calculated from sampled data?
For evenly spaced measurements, subtract the mean line from each height, take absolute values, then average them. This calculator automates centering, absolute deviation, summary metrics, and plotting.
Why does the calculator use the mean line?
The mean line represents the reference baseline for the profile. Centering points around it prevents vertical offset from distorting the roughness result and keeps the deviations physically meaningful.
What units can I use?
You can use µm, mm, nm, or any consistent unit. The output remains in the same unit system as the entered profile heights, so do not mix units within one calculation.
What is the difference between Ra and Rq?
Ra averages absolute deviations, while Rq is the root mean square of deviations. Rq gives slightly more weight to larger peaks and valleys, so it is usually equal to or greater than Ra.
Why are more profile points better?
A larger sample usually represents the surface more faithfully. Too few points can miss local peaks or valleys, which may understate actual roughness and reduce confidence in the result.
What does the graph show?
The graph displays the measured profile and the zero mean line after centering. It helps you visually inspect waviness, peak distribution, valleys, and whether the entered series looks balanced.
When should I use this calculator?
Use it during machining review, inspection, finishing validation, process comparison, or educational analysis. It is especially useful when you already have sampled height data from a profilometer or lab sheet.