## What is RA average?

What Does Ra Mean? As described in ASME B46. 1, Ra is the arithmetic average of the absolute values of the profile height deviations from the mean line, recorded within the evaluation length. Simply put, Ra is the average of a set of individual measurements of a surfaces peaks and valleys.

**What is RA measurement for surface finish?**

Ra is the arithmetic average of surface heights measured across a surface, Ra surface finish. Simply average the height across the microscopic peaks and valleys. Surface roughness can be measured by a profilometer, a surface profile measurement tool.

### How is Ra value calculated?

Ra is measured using a profilometer. This is an instrument with a stylus that travels across the surface and measures the difference in height between the peaks and valleys of the surface profile. ISO standards use the term CLA (Center Line Average), which is interpreted identically to Ra.

**How do you calculate Ra value?**

Ra is calculated as the Roughness Average of a surfaces measured microscopic peaks and valleys….That means you:

- Measure height across the microscopic peaks and valleys.
- Calculate the SQUARE of each measurement value.
- Calculate the MEAN (or average) of those numbers (squared).
- Find the square ROOT of that number.

## How do you determine Ra value?

**What is the Ra value of surface roughness?**

For simplicity, the Ra value indicates the average surface roughness for the length of the measurement performed, i.e., the average difference between peaks and valleys. To schematize what roughness is, we can imagine a two-dimensional cut of the surface.

### What does Ra measure?

What Ra measures is the average distance (or height) of the peaks & valleys from the mean line. Most drawings and prints you see will have a Ra surface finish requirement called out on it. A device called a profilometer can quickly and easily measure the surface finish of a steel bar.

**What is Ra (center line average)?**

In past years Ra was also known as Center Line Average (CLA), or Arithmetic Average (AA), but today Ra is the most commonly used surface finish parameter in the steel industry. What Ra measures is the average distance (or height) of the peaks & valleys from the mean line.

## What is 6 Ra (µin)?

A 6 Ra (µin) is a very smooth polished surface. Actual surface profile showing the Ra surface finish of 0.164 µm (6 µin microinch) on a ground & polished steel bar. Ground & polished steel bars with a 6-8 Ra µin surface finish