O Ring Chart Size: Find the Perfect Fit for Seals

Need to pinpoint an O-ring’s size quickly? Our clear ‘o ring chart size’ guide streamlines your search, offering standard and metric dimensions for an exact seal fit. Dive into an array of sizing options without the complexity.

Key Takeaways

  • O-ring size charts, including AS568 for standard sizes and metric G and A series, provide a comprehensive range of dimensions and tolerances for sealing applications in various industries.
  • Custom O-rings offer a personalized solution for unique applications without the burdens of tooling fees, and material selection is critical for meeting specific operational conditions.
  • Alternative sealing solutions like square rings and X-rings extend options for improved sealing efficiency, backed by online resources and expert assistance for optimal selection.
February 15, 2024
o ring chart size article cover

Understanding O-Ring Size Charts

o ring chart size difference

An O-ring size chart functions as a compass guiding you through the maze of standard and metric sizes, simplifying the process of identifying and selecting the perfect O-ring for your application. These size charts act as a universal language, ensuring compatibility with application-specific requirements across various industries and applications. Think of O-ring size charts as your roadmap to sealing success.

The realm of O-ring sizes is vast, with the two principal sizing systems being standard and metric. These cater to the most widely used sizes across diverse industries. Standards like AS568 for standard sizes are crucial as they serve as a guide, ensuring compatibility with different international standards. These charts, with their wide array of standard and non-standard O-ring sizes, foster greater adaptability and equip you to tackle a variety of sealing challenges.

AS568 O-Ring Standard

The Society of Automotive Engineers (SAE) has developed the AS568 standard, which acts as a beacon for establishing O-ring sizes within the United States. This system employs a dash numbering method to classify O-ring dimensions, denoting various cross-sectional diameters such as:

This standard not only specifies standard ring sizes but also sets forth tolerances for these rings. It provides guidance on permissible variations in an O-ring’s size that may arise from manufacturing processes.

Imagine yourself steering through celestial paths marked by 369 distinct constellations. Similarly expansive is the array presented by AS568’s directory of 369 standardized sizes. This extensive roster enables you to navigate with certainty among myriad options when selecting just the right sealant solution tailored to your requirements.

O-Ring Size Charts

Size C.S. Inch I.D. Inch O.D. Inch C.S. MM I.D. MM O.D. MM
001 0.040 0.029 0.109 1.02 0.74 2.78
002 0.050 0.042 0.142 1.27 1.07 3.61
003 0.060 0.056 0.176 1.52 1.42 4.46
004 0.070 0.070 0.210 1.78 1.78 5.34
005 0.070 0.101 0.241 1.78 2.57 6.13
006 0.070 0.114 0.254 1.78 2.90 6.46
007 0.070 0.145 0.285 1.78 3.68 7.24
008 0.070 0.176 0.316 1.78 4.47 8.03
009 0.070 0.208 0.348 1.78 5.28 8.84
010 0.070 0.239 0.379 1.78 6.07 9.63
011 0.070 0.301 0.441 1.78 7.65 11.21
012 0.070 0.364 0.504 1.78 9.25 12.81
013 0.070 0.426 0.566 1.78 10.82 14.38
014 0.070 0.489 0.629 1.78 12.42 15.98
015 0.070 0.551 0.691 1.78 14.00 17.56
016 0.070 0.614 0.754 1.78 15.60 19.16
017 0.070 0.676 0.816 1.78 17.17 20.73
018 0.070 0.739 0.879 1.78 18.77 22.33
019 0.070 0.801 0.941 1.78 20.35 23.91
020 0.070 0.864 1.004 1.78 21.95 25.51
021 0.070 0.926 1.066 1.78 23.52 27.08
022 0.070 0.989 1.129 1.78 25.12 28.68
023 0.070 1.051 1.191 1.78 26.70 30.26
024 0.070 1.114 1.254 1.78 28.30 31.86
025 0.070 1.176 1.316 1.78 29.87 33.43
026 0.070 1.239 1.379 1.78 31.47 35.03
027 0.070 1.301 1.441 1.78 33.05 36.61
028 0.070 1.364 1.504 1.78 34.65 38.21
029 0.070 1.489 1.629 1.78 37.82 41.38
030 0.070 1.614 1.754 1.78 41.00 44.56
031 0.070 1.739 1.879 1.78 44.17 47.73
032 0.070 1.864 2.004 1.78 47.35 50.91
033 0.070 1.989 2.129 1.78 50.52 54.08
034 0.070 2.114 2.254 1.78 53.70 57.26
035 0.070 2.239 2.379 1.78 56.87 60.43
036 0.070 2.364 2.504 1.78 60.05 63.61
037 0.070 2.489 2.629 1.78 63.22 66.78
038 0.070 2.614 2.754 1.78 66.40 69.96
039 0.070 2.739 2.879 1.78 69.57 73.13
040 0.070 2.864 3.004 1.78 72.75 76.31
041 0.070 2.989 3.129 1.78 75.92 79.48
042 0.070 3.239 3.379 1.78 82.27 85.83
043 0.070 3.489 3.629 1.78 88.62 92.18
044 0.070 3.739 3.879 1.78 94.97 98.53
045 0.070 3.989 4.129 1.78 101.32 104.88
046 0.070 4.239 4.379 1.78 107.67 111.23
047 0.070 4.489 4.629 1.78 114.02 117.58
048 0.070 4.739 4.879 1.78 120.37 123.93
049 0.070 4.989 5.129 1.78 126.72 130.28
050 0.070 5.239 5.379 1.78 133.07 136.63

It’s important to clarify a couple of points for accuracy and understanding:

  • Cross-Sectional Diameter (C.S.) and Inner Diameter (I.D.) are the primary dimensions used to select an O-ring for a given application. The Outer Diameter (O.D.) is derived from these two dimensions and is less commonly used for selection purposes but is useful for certain calculations and verifications.
  • The C.S. and I.D. measurements in inches are directly tied to the O-ring size designation (e.g., 001, 102, etc.), which are standard within the industry, particularly for AS568 standard O-rings. The conversion to millimeters (MM) provides a metric equivalent for those who work in systems or regions where metric measurements are standard.
  • The consistency in the cross-sectional diameter across different O-ring sizes (noted in your table as consistently 0.070 inches for sizes 001 through 050 and 0.103 inches for sizes 102 through 150) is indicative of how O-ring sizes are organized within the AS568 standard. Different series within the standard have specific cross-sectional diameters, allowing for a variety of inner diameters to accommodate different groove sizes.
  • This table is a simplified representation of the AS568 O-ring sizes. For each specific application, other factors such as material compatibility, temperature range, and pressure rating must also be considered to ensure the correct O-ring selection.

Dash Number System

The Dash Number System is a standardized method used to identify O-ring sizes within the AS568 standard, which is widely recognized in various industries, including automotive, aerospace, and hydraulic systems. This system simplifies the process of selecting and specifying O-rings by providing a clear and concise way to refer to the size of an O-ring based on its inner diameter (I.D.) and cross-sectional diameter (C.S.).

How the Dash Number System Works:

  • Unique Identifier: Each dash number corresponds to a specific O-ring size. The dash number serves as a unique identifier that denotes both the inner diameter and the cross-sectional diameter of an O-ring.
  • Inner Diameter (I.D.): The I.D. is the internal diameter of the O-ring, which is crucial for ensuring the O-ring fits snugly within the groove or cavity where it is installed.
  • Cross-Sectional Diameter (C.S.): The C.S. is the thickness of the O-ring, measured from one side to the other. This dimension affects how the O-ring compresses to form an effective seal.

How to Use the Dash Number System:

  • Identify Groove Dimensions: Begin by measuring the dimensions of the groove or cavity where the O-ring will be seated. This includes both the width (which correlates with the I.D. of the O-ring) and the depth (which correlates with the C.S. of the O-ring).
  • Consult a Size Chart: Use an AS568 size chart to find a dash number that matches the required I.D. and C.S. dimensions. These charts list O-rings by dash number and provide corresponding dimensions in both inches and millimeters.
  • Consider Tolerances: Keep in mind the manufacturing tolerances specified alongside each size. These tolerances indicate the allowable variance in dimensions, ensuring the O-ring can achieve a proper seal even with slight variations in size.
  • Select Material: Once you have identified the correct dash number, select an appropriate material for the O-ring based on the application’s specific requirements, such as temperature range, fluid compatibility, and pressure.
  • Verify Compatibility: Double-check the compatibility of the O-ring’s dimensions and material with the application’s conditions. Ensure that the selected O-ring can withstand the operational environment, including any chemical exposures or temperature fluctuations.

The Dash Number System streamlines the selection process for O-rings by providing a standardized set of dimensions that are easily referenced and widely understood across industries. By following this system, engineers and technicians can quickly and accurately identify the correct O-ring size for their needs, ensuring a reliable seal and optimal performance in their applications.

Explore our guide on hydraulic hose fitting types and how to identify and work with them for a seamless connection experience.

Metric O-Ring Sizes

Within the world of metric O-rings, the G series and A series stand as the definitive standard models. The comprehensive G series encompasses an astounding 445 different sizes, whereas the specialized A series provides a selection of 383 sizes tailored for aerospace use where more stringent tolerances are necessary.

When it comes to denoting ring sizes in this system, they’re typically specified by their cross-sectional diameter (CS) followed by their internal diameter (ID). For example, an o-ring marked as ‘1.00X005’ has a cross-section measuring 1 mm coupled with an inner diameter spanning 5 mm. This expansive assortment guarantees that you’ll find the perfect size to meet your sealing needs within these metric standards.

Material Considerations in the Context of O-Ring Size Chart

Choosing O-rings? Think materials and size. It’s a big deal. Here’s the lowdown on why materials matter just as much as sizing:

Materials Change the Game:

  • Chemicals: Some materials fight off chemicals better. Like Nitrile? Great against oil. Viton®? It laughs in the face of high heat and nasty chemicals.
  • Hot or Cold: Materials can take different levels of heat. Silicone is cool with a wide range, while EPDM handles heat, water, and steam like a champ.
  • Hard or Soft: The right hardness seals the deal under pressure. Soft materials are good for the easy stuff, but when the pressure’s on, you need something tougher.
  • Size Shifts: Heat, cold, and pressure can make O-rings change shape. Keep that in mind to keep your seal tight.

Choosing Right:

  • Heat Things Up or Cool Them Down: O-rings can grow or shrink with temperature changes. Pick a material that keeps it cool (or heat) to keep your seal just right.
  • Stay in Shape: Materials can get tired and squish down over time, causing leaks. Choose one that stays in shape to keep things sealed.
  • Swelling Issues: Chemicals can make materials puff up, changing the fit. Know what you’re dealing with to avoid surprises.

Customized O-rings can be crafted from various materials, including:

  • Buna-N (Nitrile)
  • Silicone
  • Teflon® (PTFE)
  • Ethylene Propylene (EPDM)
  • Kalrez® (FFKM)
  • Viton® (FKM/FPM)
  • Fluorosilicone (FVMQ/FSIL)
  • Aflas® (TFE/P)
  • Polyurethane(PU/AU)

These materials are specially tailored with distinct properties to meet the specific needs of different applications, and selections are commonly made based on these attributes.

Smart Steps for Material Choices:

  • Check the Scene: Look at what you’re working with – fluids, temperatures, and all that.
  • Chart It Out: Use compatibility charts. They’re your best friend for matching materials to your needs.
  • Certify It: Some jobs need materials with special creds, like for food or planes.
  • Talk to the Pros: Suppliers know their stuff. They can help you pick the perfect material.

Mixing material smarts with sizing know-how means O-rings that fit right and work well. This is how you nail sealing every time.

Square Rings and X-Rings: Alternative Sealing Solutions

Square Rings and X-Rings

In the realm of sealing solutions, variety is key. Beyond the well-known O-rings, one can also choose from a range of alternatives like square rings and X-rings. These variants are widely used across multiple industries due to their specialized design advantages. They offer enhanced sealing capabilities over traditional O-rings, which may lead to decreased maintenance and lower frequency of replacements.

Just as an experienced traveler has numerous tools at their disposal, so do you when it comes time to pick an appropriate seal. There’s a plethora of online information available concerning Quad-Ring Seals (another term for X-rings), Rubber X-Ring Seals, and Rubber Square-Ring Seals that showcase the breadth of options available in this field.

Square Rings

In the world of seals, square rings stand out for their unique design. Viewed from above, they appear round, while their side profile reveals a square shape that allows them to slot seamlessly into grooves made for O-rings. This means that square rings can substitute O-rings without requiring modifications in product designs or altering assembly procedures.

When it comes to sealing solutions, square rings are often more budget-friendly than alternatives, offering an economical approach to achieving a tight seal. They are particularly beneficial when used in applications with narrow sealing spaces subjected to substantial load forces due to pressure.

Square rings are favored for their adaptability and effectiveness at creating durable seals on various surface types, including those that might be uneven or non-uniform—traits that make them indispensable across many different sectors within industries.


X-rings, sometimes referred to as QUAD-Rings, are distinguished by their unique design, which enhances sealing capabilities beyond those of conventional O-rings. Their four sealing surfaces provide them with notable advantages such as:

  • Enhanced stability in dynamic applications by resisting twisting motions and reducing the risk of spiral failure.
  • A marked enhancement over traditional O-ring performance.
  • An innovative profile featuring four lobes and corresponding notches that assist in maintaining lubrication, thereby prolonging seal longevity.

X-rings are not suitable for all conditions. They are less ideal for environments involving either high-pressure or rapid dynamic movements. They excel instead under specific circumstances, including:

  • Static situations with low-pressure requirements or light dynamic action
  • Rotational movement at speeds no greater than 6.5 feet per second
  • Pressure environments below 150 psi
  • Operating temperatures ranging from -30°C up to +100°C

Under these parameters, X-rings achieve peak effectiveness, particularly within rotary mechanisms. Although operating similarly to O-rings on a radial squeeze principle when used within piston/bore type configurations, X-rings necessitate wider grooves but lesser compression force for effective sealing outcomes.

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Common O-Ring Sizing Questions

o-ring chart size questions

Navigating through the complexity of O-ring sizing is often accompanied by inquiries. Frequently asked questions concern themselves with matters such as tolerances, cross-sectional dimensions, and the diameters on both the inside and outside of an O-ring. It’s essential to grasp these elements to ensure the correct seal selection for a specific application. For example, fluctuations in temperature and pressure may lead to the expansion or contraction of the O-ring, which can alter its internal and external dimensions. Choosing suitable materials can lessen these impacts.

Exploring this subject will move you closer to mastering the art of determining proper O-ring sizes.


In the realm of O-rings, both sizes and tolerances are critical. Tolerances in O-ring specifications denote the allowable range of variation for an O-ring’s dimensions to guarantee that it can adequately serve as a seal within its intended application.

Consider tolerances to be the margin of flexibility necessary for optimal performance by an O-ring. An overly narrow tolerance might prevent proper sealing, while excessively wide tolerances could lead to the ring dislodging from its seat or being squashed. As such, grasping these tolerance parameters is crucial for the effective functioning of your seal.

Cross-Sectional Diameters

Ensuring that an O-ring has the proper cross-sectional diameter is critical, as it must match the groove where it will be seated to create optimal compression and an effective seal. The necessary sealing pressure in a specific application can only be achieved with an accurately sized cross-sectional diameter of the O-ring.

The range of cross-sectional diameters for O-rings spans from 0.040 inches to 0.275 inches, which accommodates different designs of grooves and varying demands for compression strength. Size charts for metric O-rings present details on both inner and outer diameters along with their respective cross-sectional measurements, offered in units of inches as well as millimeters—key information when pursuing a successful sealing application.

Inside/Outside Diameters

The inside and outside diameters of an O-ring must be carefully balanced, akin to a dance between yin and yang in seal dimensioning. The diameter within an O-ring ought to be marginally smaller than that of the surface it is meant to seal against, ensuring adequate compression for a tight fit. Conversely, sizing the outer diameter requires taking into account not only groove measurements but also sufficient stretch allowance when fitting.

Selecting an appropriate o ring size necessitates evaluating various aspects such as inner and outer diameters along with groove width specific to its application. Armed with knowledge regarding these parameters ensures one’s capability in finding an ideal o ring size tailored for their sealing requirements.


In traversing the realm of seals, we have examined O-ring size charts encompassing both standard and metric dimensions as well as custom options for unique applications. Our exploration has covered the detailed aspects of O-ring measurements—such as tolerances and cross-sectional diameters—together with inside and outside diameters. This knowledge is crucial whether you’re in search of a conventional O-ring or seeking out alternatives like square rings or X-rings to ensure an impeccable seal for your specific needs. Armed with these insights into sealing solutions’ sizes and characteristics, finding the ideal ring that fits seamlessly into your application becomes attainable.

Frequently Asked Questions

How do I know my O-ring size?

To ascertain the size of your O-ring, employ a caliper or micrometer to gauge both the inside diameter and the cross-section of the ring. Be aware that while measuring, recording the outside diameter is less critical.

What size is the #12 O-ring?

Utilize this data indicating that the #12 O-ring possesses an inside diameter of 5/8 inch to locate a suitable replacement for your requirements.

What size is a #9 O-ring?

An O-ring designated as #9 possesses a wall thickness of 3/32 inches, with its exterior diameter measuring 7/16 inches, and also has an inner diameter.

How do you size an O-ring?

For accurate sizing of an O-ring, ensure it is positioned on a surface that’s clean, flat, and level. Proceed to measure the cross-section (CS), inner diameter (ID), and outer diameter (OD), following the provided guidelines.

What are O-ring tolerances, and why are they important?

Tolerances for O-rings denote the allowed variations within the dimensions of an O-ring, which are critical to guarantee that it effectively fulfills its sealing role in the intended machinery.

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