Surface Roughness Chart: Ra and Rz Roughness Specification

Surface Roughness Chart- Ra and Rz Roughness Specification

Surface finish, also known as surface roughness, is critical in predicting a part’s mechanical performance. The component’s durability and performance can be negatively affected by surface imperfections because they act as crack or corrosion nucleation sites.

In addition, the roughness of a surface might be crucial in certain uses, such as cosmetic containers. These coatings improve the item’s appearance and protect it from environmental factors and wear.

Indeed, the importance of achieving a suitable surface finish extends beyond aesthetics; it directly impacts the product’s performance and reliability. When an item is visually appealing, potential buyers are naturally drawn to it, increasing its marketability.

However, a visually appealing product is not enough; it must also function as expected to satisfy customers and ensure long-term usage.

This comprehensive guide will go over every aspect of surface finish and roughness. You will not only learn how to measure them accurately, but you will also gain knowledge of the various scales and standards used in the manufacturing industry.

With this information, you can improve the quality and performance of your products, increase customer satisfaction, and stay ahead of the competition. So, let’s get started and discover the secrets of surface finish excellence!

What is Meant by Surface Finish?

Surface finish, or surface texture or topography, refers to a surface’s smoothness and overall quality. It includes minor, localized deviations from an ideal flat plane.

This term is commonly used to describe surface roughness, and it is an important factor to consider in technical drawings for mechanical parts, particularly when components must fit closely together, move against each other, or form a tight seal.

What Role Does Surface Finish Play in Engineering Processes

The terms “surface finish” and “surface roughness” are frequently used interchangeably in machine shops, but they actually refer to four distinct characteristics: lay, waviness, roughness, and flaws.

Let’s go into each of these component details.


The main pattern or direction of a surface finish is called the lay. It is comparable to the “grain” of the surface, and its direction can considerably influence the performance and look of the item in some applications, such as bearings.

Where the direction of the surface texture affects friction and wear, effective lay control is crucial.


Waviness represents the longer wavelength deviations in the surface profile. These variances are bigger than those of roughness elements but fewer than those of defects.

Waviness can influence the fit and function of mating pieces as well as the overall integrity of the assembly.


Roughness, commonly acknowledged as the most important surface finish feature, refers to minor differences in the roughness of a surface.

These minor imperfections can impact friction, wear, and contact between mating components. It is critical to achieve the desired roughness to meet specific functional requirements.


Any irregularities or defects on the surface that deviate from the desired form or shape are considered flaws. These can include scratches, pits, cracks, or other flaws that may compromise the structural integrity or aesthetics of the part.

What Role Does Surface Finish Play in Engineering Processes?

What Role Does Surface Finish Play in Engineering Processes

Surface finish is critical in product design because it significantly impacts the parts’ overall performance, function, quality, and aesthetics. Let us look at some compelling reasons why these factors are critical:


The visual appeal of the component and the final product is directly related to the texture and quality of its surfaces. A visually appealing design increases the product’s appeal and attracts customers, contributing to its market success.

Friction and Wear

Surface texture affects frictional characteristics and material wear. A rough surface has more friction and wear than a smooth one. This knowledge is critical for optimizing the product’s durability and reliability.

Production Processes

Manufacturing processes depend on surface texture and roughness. Depending on the production procedure, some surface treatments may be more costly.

It’s better to choose a process that will be required no to minimal secondary operation to get the desired surface finish.

Adhesion and Coating

Surface roughness influences adherence to other materials or coatings. A rough surface provides good bonding. In contrast, a smoother surface with reduced surface area may not adhere adequately.

Specific Usability

The surface roughness is critical in some areas, such as aerospace. Understanding these functional criteria guarantees that the product will fulfill the specific needs of its intended use.

Surface roughness and texture are critical aspects of product design that should never be overlooked.

How to Determine Surface Roughness?

How to Determine Surface Roughness

You can choose different approaches from several measuring systems for a precise surface roughness evaluation. These systems include:

Direct Measurement Methods

This technique directly measures surface roughness using a pointer or a stylus. The stylus is drawn perpendicular to the surface, and a registered profile is used to determine roughness parameters.

Non-contact Methods

Unlike direct measurement methods, non-contact techniques, such as optical or laser-based systems, use advanced technology to measure surface roughness without physically touching the surface.

These non-contact methods are especially beneficial for sensitive materials.

Comparison Methods

Comparing the surface to known standards or reference surfaces is a comparison method. This method allows for a quick and simple assessment of surface roughness in real time.

In-process Methods

In-process methods are used to monitor and control surface roughness during the manufacturing process. Manufacturers can make timely adjustments and ensure that the final product meets the desired specifications.

Here different techniques are used such as ultrasound, machine vision, and magnetic inductance.

The most appropriate measuring system is determined by factors such as material type, surface area, precision requirements, and the specific characteristics of the surface under evaluation.

Engineers and machinists carefully choose the appropriate method to ensure accurate and reliable measurements, ultimately contributing to the manufactured components’ overall quality and performance.

What are Surface Roughness Terms and Symbols?

When searching for machining surface finish symbols, you’ll find several abbreviations like Ra, Rmax, Rz, etc. These abbreviations represent essential units used in measuring surface finish, each serving a distinct purpose in evaluating the roughness of a surface.

Ra – Average Area Roughness

Ra parameter computes the mean line average roughness of the roughness profile. Ra is obtained by dividing the evaluation length by the area between the roughness profile and its centerline.

The evaluation length comprises five sample lengths equaling one cutoff length.

Ra is common roughness measuring technique due to its relative ease of measurement (notably in the analog era). This simplicity made it widely accessible and applicable across various industries.

Ra doesn’t adequately represent surface roughness. Surfaces with the same Ra value can have varied surface roughness/texture (see illustration below). Additional parameters are required to discern these subtleties and make more informed decisions.

What are Surface Roughness Terms and Symbols

Rmax – Vertical Distance from Highest Peak to Lowest Valley

Rmax is the maximum vertical distance between the highest point and the lowest valley on the surface. Scratches and burrs, for example, can be easily detected with this metric, but they may go undetected with average-based measurements like Ra.

By capturing the extreme points of the surface, Rmax offers valuable insights into the presence of irregularities that could affect performance and durability.

Rz – Average Maximum Height of the Profile

Rz doesn’t measure from the centerline as Ra does. Instead, it averages the five biggest differences between peaks and valleys over five sampling lengths.

Rz is sensitive to surface variations in height because of its emphasis on extremes, making it more useful than Ra.

ISO Surface Finish Symbols and Callouts

ISO Surface Finish Symbols and Callouts
ISO Surface Finish Symbols and Callouts

ISO Surface Finish Symbols and Callouts

Surface Roughness Chart

The machining surface finish chart helps manufacturers assure quality and accuracy. Manufacturers should use the reliable machined surface finish inspection technique to produce high-quality goods.

This decision directly impacts the product’s overall performance and functionality.

Surface Roughness Chart

Surface Finish Conversion Chart

Utilizing the surface finish conversion chart empowers manufacturers to optimize their production processes, streamline quality control, and uphold stringent standards of excellence.

This tool is a common language that bridges the gap between different measurement systems, making it easier for engineers and technicians to collaborate effectively and ensure that the product meets the desired specifications.

Moreover, the surface finish conversion chart facilitates communication and collaboration across international boundaries, where various countries might employ different surface finish measurement standards.

By adopting this universal chart, manufacturers can engage in seamless global partnerships and access a broader product market.

The table below converts surface finish or Roughness between Ra, Rz, and RMS indicators.


Ra = Roughness average (micro meters & inches)
RMS = Root Mean Square (micro-inches)
CLA = Center Line Average (micro-inches)
Rt = Roughness total  (microns)
N = New ISO (Grade) scale numbers
Cutoff Length = Sample length.

Surface Finish Conversion Chart

Following the surface finish ‘cheat sheet’ is an extremely useful tool for better understanding the various surface finishes available.

Cheat Sheet


Acquiring precise surface roughness in modern manufacturing can be costly. As a result, it is critical to use optimal finishing processes to treat the surfaces of manufactured parts.

Understanding how various materials harden and react to finishing processes enables you to make informed decisions. Rather than using a one-size-fits-all approach, you can tailor your surface finishing strategies to the characteristics of the material.

This knowledge aids in streamlining production, cost control, and attaining the desired surface qualities.

Kemal offers affordable, high-quality surface finishing. Our professionals are well-versed in surface finish standards. We strive to exceed your expectations with our industry expertise.

When you entrust your project to Kemal, you can rest assured of full dimensional inspection reports, ensuring the precision and accuracy of the final product.

We tailor our services to suit your unique requirements, ensuring that your products receive the finest treatment to achieve the desired surface finish.

Customer satisfaction is at the heart of everything we do, and our dedication to excellence is evident in the quality of our services.

Whether you require on-demand finishing solutions or have specific surface finish specifications, Kemel has the expertise and capabilities to deliver outstanding results.

So, if you seek a reliable partner for your surface finishing needs, Kemel is the name to trust. Contact us today to discuss your requirements, and together, we will elevate the quality and performance of your products through the required surface finishes.


Surface roughness can be determined using different devices, including touch-assisted (stylus) and touchless (sound, ultrasonic, or laser), using standards like Ra, Rz, Rmax, etc.

Surface finishing doesn’t require a chart. Using a standard chart, you can compare the roughness of one part’s surface to that of others.

All that is required is to measure the surface and compare the results with the chart. Doing so can quickly assess the surface quality and make improvements where needed.

Surface finishing charts help manufacturers and workers with surface preparation. Learning to use the chart effectively doesn’t require significant time or expertise.

By familiarizing themselves with the chart’s key elements, individuals can confidently evaluate surface roughness and make informed decisions to enhance the final product’s quality.

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