How do I Determine what Hydraulic Hose I am working with?

Sizing is the most basic and essential factor in hydraulic hose selection. Sizing specifications for hydraulic hose include inner diameter, outer diameter, and length.
Outer diameter (O.D.) measures the entire span of the hose cross-section, including the tube, reinforcement, and cover. The difference between the O.D. and I.D. is the thickness of the hose wall. Outer diameter is essential for sizing industrial hose to appropriate fittings and system components.
Inner diameter (I.D.) is the span of the space in a circular hose cross-section that affects the fluid flow velocity within the hose. A hose with an oversized I.D. will result in sluggish system performance, while an undersized I.D. can cause excessive pressure drops, leaks, and system damage.
The length of the hydraulic hose defines its maximum reach between endpoints. Increasing length can also increase the pressure drop in the system because hose length is a function of head loss due to friction.
People new to the hydraulic industry often ask what hose dash size means. Simply put, a dash size refers to an I.D. of a hydraulic hose or fitting in 1/16″ increments. For example, -6 hose would indicate a hose with an I.D. of 6/16″ – or 3/8″.
Hoses are measured by inside diameter, unlike tubes, which are measured by outside diameter. As a matter of fact, that is how the hoses and tubes are differentiated.