O-Ring Size Chart - BS 1806

24 April 2026

Verified by Rachel Mayfield, Supply Chain Analyst - April 2026

Close-up of an artisan shaping a handmade ring on a wooden mandrel tool.
Photo by Maksim Goncharenok on Pexels

BS 1806 O-ring sizes from BS001 to BS050, showing inside diameter (ID) and cross-section (CS) in both metric and imperial. O-Ring Size Chart - BS 1806 BS 1806 is the British Standard O-ring sizing system, still widely used across UK engineering despite the adoption of ISO 3601 metric sizes. These dimensions are identical to the AS568 (US) sizing system. Cross-sections step from 1.27 mm to 1.78 mm at BS004, and to 2.62 mm at BS029.

BS Size ID (mm) CS (mm) ID (inch) CS (inch)
BS001 1.07 1.27 0.042 0.050
BS002 1.42 1.52 0.056 0.060
BS003 1.78 1.52 0.070 0.060
BS004 2.57 1.78 0.101 0.070
BS005 2.90 1.78 0.114 0.070
BS006 3.68 1.78 0.145 0.070
BS007 4.47 1.78 0.176 0.070
BS008 5.28 1.78 0.208 0.070
BS009 6.07 1.78 0.239 0.070
BS010 6.86 1.78 0.270 0.070
BS011 7.65 1.78 0.301 0.070
BS012 9.19 1.78 0.362 0.070
BS013 10.77 1.78 0.424 0.070
BS014 12.37 1.78 0.487 0.070
BS015 13.94 1.78 0.549 0.070
BS016 15.54 1.78 0.612 0.070
BS017 17.12 1.78 0.674 0.070
BS018 18.72 1.78 0.737 0.070
BS019 20.30 1.78 0.799 0.070
BS020 21.89 1.78 0.862 0.070
BS021 23.47 1.78 0.924 0.070
BS022 25.07 1.78 0.987 0.070
BS023 26.64 1.78 1.049 0.070
BS024 28.24 1.78 1.112 0.070
BS025 29.82 1.78 1.174 0.070
BS026 31.42 1.78 1.237 0.070
BS027 33.00 1.78 1.299 0.070
BS028 34.59 1.78 1.362 0.070
BS029 37.77 2.62 1.487 0.103
BS030 39.34 2.62 1.549 0.103
BS031 40.94 2.62 1.612 0.103
BS032 42.52 2.62 1.674 0.103
BS033 44.12 2.62 1.737 0.103
BS034 45.69 2.62 1.799 0.103
BS035 47.29 2.62 1.862 0.103
BS036 48.90 2.62 1.925 0.103
BS037 50.47 2.62 1.987 0.103
BS038 53.64 2.62 2.112 0.103
BS039 56.82 2.62 2.237 0.103
BS040 59.99 2.62 2.362 0.103
BS041 63.17 2.62 2.487 0.103
BS042 66.34 2.62 2.612 0.103
BS043 69.52 2.62 2.737 0.103
BS044 72.69 2.62 2.862 0.103
BS045 75.87 2.62 2.987 0.103
BS046 82.22 2.62 3.237 0.103
BS047 88.57 2.62 3.487 0.103
BS048 94.92 2.62 3.737 0.103
BS049 101.27 2.62 3.987 0.103
BS050 107.62 2.62 4.237 0.103

How to use the BS 1806 O-ring size chart

Measure the inside diameter of the groove or housing with calipers. Then measure the cross-section (cord diameter) of the existing O-ring. Match both dimensions to this table to find the BS reference number. When ordering replacements, always specify the BS number rather than just dimensions to avoid confusion between metric and imperial sizes.

For gland design, the O-ring ID should be slightly larger than the piston diameter (for piston seals) or slightly smaller than the bore diameter (for rod seals). Standard squeeze is 10-30% of the cross-section for static seals and 10-20% for dynamic seals.

Related standards

References

  1. BS 1806:2006 - Dimensions of toroidal sealing rings (O-rings)
  2. AS568B - Aerospace size standard for O-rings

Where this data comes from: Supplier listings are verified against Companies House public records. Product specifications reference published ISO, BS, and DIN standards. Trade body data is sourced from official member directories.

Frequently Asked Questions

What is a BS 1806 O-ring?

BS 1806 is the British Standard sizing system for O-rings, defining inside diameters and cross-sections for standard sizes BS001 through BS932. The sizes originate from imperial measurements and are identical to the AS568 (US) system. It's the most common O-ring sizing system used in UK industry.

Are BS 1806 and AS568 O-ring sizes the same?

Yes. BS 1806 and AS568 O-ring sizes share identical dimensions. A BS110 is the same O-ring as an AS568-110. The only difference is the naming convention. Both use imperial-origin dimensions expressed in inches and millimetres.

How do I measure an O-ring to find its BS size?

Lay the O-ring flat without stretching it. Measure the inside diameter (ID) across the inner opening with calipers. Then measure the cross-section (CS) by compressing the ring slightly and measuring its thickness. Match both values to the BS 1806 chart. Used O-rings may be slightly stretched, so measure a new one if possible.

What does the O-Ring Size Chart - BS 1806 provide?

The O-Ring Size Chart - BS 1806 provides detailed dimensions for O-rings from size BS001 to BS050, listing inside diameter (ID) and cross-section (CS) in both metric and imperial units.

What are the CS sizes for BS004 and higher?

The O-Ring Size Chart - BS 1806 shows that starting at BS004, the cross-section size increases to 1.78 mm (approximately 0.070 inches).

How do you choose between ISO 3601 metric sizes and BS 1806 for O-rings?

The choice depends on compatibility with existing systems; BS 1806 is still widely used in the UK despite the adoption of ISO 3601, due to its historical usage.

What are some common variants of O-ring sizes listed under BS 1806?

Common variants include different cross-section sizes stepping from 1.27 mm to 1.78 mm at BS004 and further increasing to 2.62 mm at BS029.

Where can UK engineers find suppliers for O-rings based on the BS 1806 standard?

Engineers in the UK can look for suppliers who specialize in industrial rubber products, such as Parker O-Ring Division or Beswick Engineering Company Ltd., which stock O-rings conforming to the BS 1806 standard.

What is the cost and availability of O-rings according to BS 1806?

The cost varies based on size and material; typically, larger sizes like BS029 are more expensive due to higher material usage. Availability is generally good through major UK suppliers, though custom or less common sizes may have longer lead times.

What is the significance of AS568 (US) sizing in relation to BS 1806?

The O-Ring Size Chart - BS 1806 dimensions are identical to those of the AS568 (US) sizing system, facilitating interchangeability between UK and US engineered systems.

References