Updated: 2 September 2026
Hydraulic Hose Sizes Explained: Dash Sizes, ID & Hose Identification
Hydraulic hose size normally refers to the hose’s internal diameter, or bore. Choosing the correct size matters because hose diameter affects fluid velocity, pressure loss, heat generation, fitting compatibility and overall hydraulic performance.
Hydraulic hoses are commonly identified using dash sizes such as -04, -06, -08, -10, -12 and -16. In many common hydraulic hose ranges, the dash number corresponds to the nominal hose bore in sixteenths of an inch.
This guide explains hydraulic hose dash sizes, internal and outside diameter, hose laylines, fitting compatibility and how to identify the correct hose when a replacement is needed.
For a broader introduction to hose construction, reinforcement and applications, see our hydraulic hoses comprehensive guide.
Quick Answer:
What do hydraulic hose sizes mean? Hydraulic hose size normally refers to the nominal inside diameter of the hose. Many hydraulic hose ranges use dash sizes where the number represents sixteenths of an inch. For example, a -08 hose commonly corresponds to a nominal 8/16 inch, or 1/2 inch, internal diameter.
Hydraulic Hose Dash Sizes Explained
Dash sizing is widely used in hydraulic hose identification.
For many common hydraulic hose types:
- -04 = 4/16 inch = 1/4 inch nominal bore
- -06 = 6/16 inch = 3/8 inch nominal bore
- -08 = 8/16 inch = 1/2 inch nominal bore
- -10 = 10/16 inch = 5/8 inch nominal bore
- -12 = 12/16 inch = 3/4 inch nominal bore
- -16 = 16/16 inch = 1 inch nominal bore
Important
Dash sizing is a useful identification system, but the actual hose should still be checked against the manufacturer’s hose series and specification. Do not assume that outside diameter or fitting appearance alone confirms the hose size.
Common Hydraulic Hose Size Chart
| Dash Size |
Nominal Bore |
Approx. Metric Equivalent |
| -04 |
1/4 inch |
6.4 mm |
| -06 |
3/8 inch |
9.5 mm |
| -08 |
1/2 inch |
12.7 mm |
| -10 |
5/8 inch |
15.9 mm |
| -12 |
3/4 inch |
19.1 mm |
| -16 |
1 inch |
25.4 mm |
Nominal dimensions are for identification guidance. Always check the actual hose manufacturer’s specification for the selected hose series.
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Internal Diameter vs Outside Diameter
The internal diameter (ID) is the bore through which hydraulic fluid flows.
The outside diameter (OD) is the total external diameter of the completed hose, including the tube, reinforcement and outer cover.
Internal Diameter
The nominal hose bore. This is the key size when considering fluid velocity, flow requirements and hydraulic hose identification.
Outside Diameter
The overall external width of the hose. It varies according to hose construction, reinforcement and cover thickness.
Do Not Size a Hydraulic Hose by Outside Diameter
Two hoses with similar outside diameters can have different internal diameters, reinforcement and working-pressure capabilities. Hose identification should use the layline, manufacturer’s data and fitting information where possible.
Why Does Hydraulic Hose Size Matter?
Correct hose sizing helps the hydraulic system move the required amount of fluid without creating unnecessary restriction.
A hose that is too small for the required flow can increase fluid velocity and pressure drop and may contribute to unwanted heat generation.
Correct sizing helps support:
- Appropriate hydraulic fluid velocity
- Acceptable pressure loss
- Correct actuator speed
- Suitable hose routing
- Correct fitting selection
- Reliable machine operation
A hose should also be selected for its required working pressure, fluid compatibility, temperature range, bend radius and operating environment.
See our hydraulic hose pressure ratings guide for more information about pressure selection.
Can a Hydraulic Hose Be Too Small?
Yes. If the hose bore is too small for the required flow, the restriction can increase pressure loss and fluid velocity.
Possible effects can include:
- Reduced actuator performance
- Higher pressure losses
- Additional heat generation
- Higher fluid velocity
- Reduced system efficiency
The correct hose size therefore depends on the actual hydraulic system rather than simply matching a hose that looks similar.
Can a Hydraulic Hose Be Too Large?
A larger hose is not automatically better.
An unnecessarily large hose may:
- Be harder to route
- Require different fittings
- Need more installation space
- Have a larger minimum bend radius
- Increase hose and fitting weight
- Be unsuitable for the original machine design
The objective is to select the hose size that suits the required flow and system specification.
How Do You Identify Hydraulic Hose Size?
There are several useful ways to identify an existing hydraulic hose.
01 — READ THE HOSE LAYLINE
Check the printed information along the hose cover for manufacturer, series, size and pressure information.
02 — IDENTIFY THE DASH SIZE
Look for a recognised hose-size designation where it appears in the hose specification.
03 — CHECK THE FITTINGS
Identify fitting type, thread, size and sealing method.
04 — CHECK MACHINE INFORMATION
Use the equipment specification or parts information where available.
05 — CONFIRM BEFORE ASSEMBLY
Where identification is uncertain, have the hose and fittings checked by a hydraulic hose specialist.
Hydraulic Hose Markings & Laylines
Many hydraulic hoses have printed information running along the outer cover. This is commonly referred to as the hose layline.
Depending on the manufacturer and hose series, the layline may include:
- Manufacturer
- Product or hose series
- Nominal hose size
- Working-pressure information
- Applicable SAE, EN or other standard
- Manufacturing or batch information
If the layline is still visible, it can provide valuable information when sourcing a replacement.
Read our full hydraulic hose layline guide for more detail.
Does Hydraulic Hose Size Have to Match the Fitting Size?
The hose and coupling must be compatible as a complete assembly.
Correct hose bore does not by itself confirm that a fitting is suitable.
The assembly must also account for:
- Hose series
- Coupling design
- Hose size
- Thread type
- Connection size
- Sealing method
- Working-pressure requirements
Common connection families include:
- BSP
- JIC
- ORFS
- Metric
- Flange connections
See our hydraulic hose fittings guide for identification of common BSP, JIC, ORFS and Metric fittings.
Hose & Coupling Compatibility Matters
A hydraulic hose assembly should use hose and coupling components that are approved as a compatible system. Do not assume that a fitting that physically fits a hose is suitable for crimping or pressure service.
Can You Measure a Hydraulic Hose to Identify Its Size?
Measurement can help, particularly when hose markings are missing, but it must be done carefully.
When an old hose is removed and safely depressurised, useful information can include:
- Internal hose bore
- Fitting thread diameter
- Fitting type
- Overall hose length
- Fitting orientation
However, measurement alone does not identify the hose’s reinforcement, pressure capability or material specification.
For practical identification guidance, see how to measure a hydraulic hose.
Common Hydraulic Hose Sizing Mistakes
- Choosing hose by outside diameter
- Assuming two similar-looking hoses have the same bore
- Ignoring the hose layline
- Using the wrong fitting or thread
- Ignoring flow requirements
- Ignoring working-pressure requirements
- Not checking fluid or temperature compatibility
- Ignoring minimum bend radius
- Failing to consider routing space
- Replacing a hose without checking why the previous one failed
Correct Size, Correct Specification
Hose bore is only one part of hose selection. A safe and reliable hydraulic hose assembly also requires the correct pressure capability, fittings, fluid compatibility, temperature rating, bend radius and routing.
Need Help Identifying a Hydraulic Hose Size?
Completely Hydraulic can help identify hydraulic hose size, fittings, hose specification and replacement options.
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Hydraulic Hose Size FAQs
What does hydraulic hose dash size mean?
For many common hydraulic hose ranges, the dash number represents the nominal hose inside diameter in sixteenths of an inch. For example, -08 commonly represents 8/16 inch, or 1/2 inch nominal bore.
Is hydraulic hose size based on inside or outside diameter?
Hydraulic hose size normally refers to nominal inside diameter or bore. Outside diameter varies according to hose construction, reinforcement and outer cover.
What size is a -06 hydraulic hose?
A -06 hydraulic hose commonly has a nominal bore of 6/16 inch, which is 3/8 inch or approximately 9.5 mm.
What size is a -08 hydraulic hose?
A -08 hydraulic hose commonly has a nominal bore of 8/16 inch, which is 1/2 inch or approximately 12.7 mm.
How do I know what size hydraulic hose I need?
Check the hose layline, manufacturer’s hose series, dash size, fitting type and machine information. Where identification is uncertain, have the hose assembly checked before replacement.
Can the wrong hydraulic hose size cause problems?
Yes. A hose that is too small for the required flow can increase fluid velocity, pressure loss and heat generation. The hose must also meet the correct pressure, temperature, fitting and routing requirements.
Can I identify hydraulic hose size from the outside diameter?
No. Outside diameter alone is not a reliable way to identify hydraulic hose bore because hose construction and reinforcement vary between hose types and manufacturers.
Does the hydraulic hose size have to match the fittings?
The hose, coupling and fitting connection must form a correctly specified and compatible hose assembly. Hose bore alone does not determine whether a coupling or fitting is suitable.
