What Size is the O-Ring Fitted to a Garden Hose?

Last modified on April 28th, 2025

It can be a right pain when water starts leaking around the connector on a garden hose. Usually the o’ring has disintegrated, or the hose connection has started coming adrift.

The physical hose connection is often quite easy… You can tighten it up.

But if the o-ring has broken, or become perished. You will need to get a new one.

But, what size is the o-ring..?

Topics:

• Garden Hose O’Ring Size:
• O’Ring Properties & Temperature Range:
• How to Measure O’Rings:
• Buying O’Rings:
• Gallery:

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Garden Hose O’Ring Sizes:

The standard 1/2″ garden hose connectors and fittings, (often quoted as 12mm, 12.5mm or 12.7mm in metric sizes) have the following o-ring size:

O-Rings Sizes for 1/2″ Garden Hose & Their Fittings

Hose Size

Unit

Outside Dia (OD)

Inside Dia (ID)

Cross Section (CS)

12.5mm or 1/2″

mm

16

10

3

Inches (Fraction)

5/8″

7/16″

7/64″

Inches (Decimal)

0.630

0.394

0.118

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O’Ring Types & Their Properties:
(for a Garden Hose):

The Viton & EPDM (also known as EP & EPM) type o’rings appear to have a lot of good qualities, due to their resistance to heat and wear. However, the EPDM o’ring copes well in direct sunlight, and is often cheaper…

O’Ring Types & Their Properties (For a Garden Hose)
Properties	– Legend –
	X  Don’t use,   X  Poor,   ✔  Good,   ✔  Great
	Garden Hose O’Rings
	1	2	3	4
	EPDM Ethylene	FKM Viton®	NBR Nitrile	S Silicone
Cost	+	+++	++++	++
Water	✔	✔	x✔	x
Sunlight (UV)	✔	✔	x	✔
Steam	✔	✔	x✔	x✔
Cold	✔✔	x	✔	✔
Heat	✔	✔	✔	✔
Air			✔
Brake Fluid	✔	x	x	x
Hydraulic	x		✔	x
Oil	x	✔	✔	x✔
Fuel	x	✔	x	x
Silicone Oils	✔	✔	✔	x
Acid	✔	✔	x	x✔
Acetone		x	x
Alcohol	✔		✔
Alkalis	✔
Chemical	✔	✔	x✔	x✔
Solvents	x
Tear	✔✔	x✔	x	x
Abrasion	✔✔	✔	✔	x
Hardness	40 to 90	50 to 95	40 to 90
Temperature Range °F	-60 to +350	-15 to +420	-40 to +250	-100 to +450
Temperature Range °C	-50 to +150	-25 to 210	-40 to +121	-60 to +230

Notes:

• EPDM rubber may be best suited for garden hose o-rings, as EPDM will resist breaking down in sunlight. EPDM – Ethylene Propylene Diene Monomer (also known as EP, EPM).
• Generally most hose connectors are the same size… But there may be some slight differences between different manufacturers.
• Viton has a low compression and has a high temperature and chemical resistance. Viton is the main choice when using with oils and fuels. Viton should be used when in contact with E10 Petrol, as the higher Ethanol content is detrimental to Nitrile Butadiene Rubber (NBR), causing it to swell and become more brittle.

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How to Measure an O’Ring:

When ordering O’Rings, you can use the BS or AS reference number, (e.g. BS-012, or AS-012). Or, you can just use the measurements…

• ID = Internal Diameter.
• OD = Outside Diameter.
• CS = Cross Section, (this is the same as W).
• W = Width (the O’Ring thickness, or ‘wire’ size).

When buying an O’ring, they will often ask for either the…

Internal Diameter (ID) & the Cross Section (CS)

or

Outside Diameter (OD) & the Internal Diameter (ID)

As any combination of two measurements will give you the size of an o-ring. For example…

(Outside Diameter (OD) – The Internal Diameter (ID)) / 2 = The Cross Section (CS)

(OD – ID) / 2 = CS

More Detail on Measuring an O’Ring:

To get the Outside Diameter:

Use the… Internal Diameter (ID) & Cross Section (CS):

ID + (CS + CS)    =   OD

To get the Inside Diameter:

Use the… Outside Diameter (OD) & Cross Section (CS):

OD – (CS + CS)    =   ID

To get the Width (O’Ring Thickness, or ‘Wire’ Size):

Use the… Outside Diameter (OD) & Internal Diameter (ID):

(OD – ID) / 2    =    CS

Notes:

• Beware when using measurements. The size is often defined by either the Internal Diameter (ID), or the Outside Diameter (OD) and the o-ring thickness (‘wire’ size). Sometimes suppliers will offer both the ID and OD measurements for you to check (but not always). So check you’re using the correct measurements (ID or OD?).
• A manufacturer may use different colours to indicate the different types of o-ring. However, the colour doesn’t always indicate the type of o-ring it is? O-rings can be manufactured in any colour you want, therefore always check the type, don’t rely on visual ‘colour’ identification.
• Don’t forget, o-rings are often fitted to provide a seal. Therefore the Internal Diameter (ID) may need to be ‘snug’ fit, and the Outside Diameter (OD) a ‘proud’ fit.
• Old o-rings may not be the same size as what was originally fitted, as they may have stretched, or been flattened in use. However, an old o-ring can give a good indication of the size needed.
  • ll always be slightly bigger than the diameter of the item being measured.
  • And slightly smaller than the groove being measured.
  • This is so the o-ring forms a seal.

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Buying O’Rings:

The cheapest method of buying o-rings is often quoting the size and quantity you need, rather than buying a small pre-packaged quantity from a branded garden hose manufacturer…

Don’t forget to ask for EPDM rubber o-rings as they will last a lot longer in sunlight.

If you’re not sure what you need, sometimes it’s a good idea to have a look? The list below may give you an idea of what’s available, what to look for, and how much the part might cost…

Garden Hose Connector O-Rings and Measurement Tools:

Garden Hose Connector O-Ring Prices
Location	Item
UK	O-Rings
	Digital Micrometer
USA	O-Rings
	Digital Micrometer
AUS	O-Rings
	Digital Micrometer
CAN	O-Rings
	Digital Micrometer
IRL	O-Rings
	Digital Micrometer

Notes:

• To find exactly what you’re looking for, you may have to enter the size of the o-ring, or enter text such as ‘garden hose’, as each supplier may use different text in their listing…
• When entering the size of an o-ring as a search term, a good place to start is using the Cross Section (CS) measurement, as this is a consistent size within a listing. Don’t add the other measurements yet, as this may over limit the results (some suppliers list a range of sizes in their listing dictated by the CS).

Hope this helps…

Image Gallery:

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