Calculating Hydraulic Hose Dimensions In 3 Easy Steps

Determining which spare parts your hydraulic system requires isn’t always easy. A mistake made at the stage of hydraulic hose dimension calculation can affect the bottom line in an unfortunate manner.

Ideally, all dimensions should be calculated by a professional. If you don’t have an opportunity to ask for expert assistance, there are some things you can do on your own.

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At Hydrastar, our engineers are always ready to make measurements in order to supply the ideal spare parts for your system. Here is a simple way to calculate hydraulic hose dimensions.

1) Learn The Basics

In order to start calculating hydraulic hose dimensions, you need to know the following parameters.

  • Outer (outside) diameter – The measurement of the entire hose cross-section, including the wall thickness. Marked OD on the picture.
  • Inner (inside) diameter – The measurement of empty space inside the hose, without the wall thickness parameter. Marked ID on the pic.
  • Length of the hose –The length of the hose is important to setting the pressure in the system. The longer the house is the more the pressure can drop.

In the majority of catalogues, the inner diameter of the hose is mentioned as its size. On the other hand, for tube sizing, the outer diameter is used.

2) Find Out About The Dash Size

Dash size or dash number is a parameter you will often see used in the hydraulic system industry. In fact, dash size is just another term for the inner diameter of a pipe.

Generally, you will find dash size parameter mentioned in 1/16’’ increments. For example:


  • Dash size -1 = inner diameter 1/16’’ (1.6 mm)
  • Dash size -2 = inner diameter 2/16’’ or 1/8’’ (3.2 mm)
  • Dash size – 3 = inner diameter 3/16’’ (4.8 mm)

Simply speaking, dash is the hose’s inner diameter written in sixteenth of an inch.

3) Read The Nomogram

A nomogram is designed to help you determine all the hydraulic hose dimensions if you know just two of them. If you know the desired flow rate and the required flow velocity, you can find out the hose of which dash size you need for your system. Or if you know the flow velocity and the dash size, you can determine the flow rate.

Nomograms are designed for fast value determination. All you have to do is draw a straight line from one known parameter to another. Then the line will either cross the third parameter or you’ll need to finish drawing the straightedge line until it reached the next column.

Hydraulic hose dimensions calculation doesn’t seem complicated at first. However, there may be different nuances which can lead to errors. We recommend asking for professional assistance with dimension evaluation in order to avoid mistakes.

At Hydrastar, we don’t just offer a big variety of spare parts for your hydraulic system, we are always ready to help you understand which parts are best suited for your project. For more information about hydraulic pipes and minimising downtime, please download our free e-book How To Minimise Downtime With Pneumatic Plant & Machinery.