Short answer
Inside diameter denotes the flow path, outside diameter the outer envelope, and overall length the assembly length between two defined references. These three dimensions cannot be used interchangeably. The cut length of the hose must be defined separately from the overall length of an assembly with fittings on both ends.
Technical explanation
The nominal size printed on a hose does not mean a caliper will find the same value under every condition. Manufacturing tolerance, measurement method and the shape of the cross-section matter. In particular, an outside diameter measurement taken by squeezing a soft hose can be misleading. In an assembly, the end-to-end length differs from the length between sealing surfaces; for elbow ends, the measurement may be given relative to the elbow centerline or another drawing reference. For this reason, the definition of the dimension should accompany the number.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Inside diameter / ID | Flow bore; nominal definition and measurement tolerance are recorded separately. |
| Outside diameter / OD | Outer envelope including the sleeve; used in selecting clamps and pass-through clearance. |
| Overall length / OAL | Start and end references marked on the drawing for the finished assembly. |
| Cut length | Length of the hose piece before assembly; a field separate from the fitting contribution. |
How is it assessed in practice?
As an example, suppose a request says only '1 inch, two meters, fittings on both ends'. Does one inch refer to the hose inside diameter or the fitting thread? Is two meters the hose to be cut or the length of the finished assembly? Before production, separate these two ambiguities into distinct fields on the drawing. Record the measurement date and method next to the sample measurement. Do not let a used, stretched or damaged sample replace the toleranced drawing of the new product.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Can I calculate the inside diameter from the outside diameter?
It cannot be calculated reliably without knowing the wall thickness and construction. Base it on the product code or a verified dimensional drawing; estimating the product family from the outside diameter is not dimensional verification.
Source coverage
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S021
Selecting a hose assembly? Remember STAMPED Swagelok Bangalore · accessed 2026-10-19 Size; Temperature; Application; Material; Pressure; End Connections; Delivery
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S024
Hose and Flexible Tubing, MS-01-180 Swagelok · accessed 2026-10-19 PDF pages 4–5 / printed 253–254: Nomenclature; pages 8–9: selection, installation and use