To measure a hydraulic hose for replacement, read the layline or measure the inside diameter (I.D.) and convert it to a dash size, then record the overall length, both fitting ends, and the pressure rating. A replacement hose must match the original’s size, length, fittings, and pressure rating. A hose that is too small can restrict flow, and the wrong fitting will not seal.
This guide covers each measurement in order, starting with the safety steps for removing the old hose, so you can match it to the correct replacement for your machine.
Start With the Information Already on the Hose
Hydraulic hose is sized by its inner diameter (I.D.). The first place to check is the layline, the printed text that runs along the side of the original hose. A layline commonly shows the hose series, the size, and the pressure rating.
Wipe the hose clean and read the full length. Oil, dirt, and abrasion can hide the print. If the layline is worn off or painted over, measure the I.D. as described in Step 1 below.
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Pro Tip: Take a picture of the layline and the hose routing before removal. A clear photo of the hose in place makes it easier to confirm length, bends, and end orientation later. |
Safety Steps Before You Remove a Hose
The I.D. and length are measured after the hose is off the machine, so the safety steps come first. Trapped fluid can still be under pressure after the engine stops.
Ohio State University Extension notes that trapped fluid pressure can be more than 2,000 psi and that pressurized fluid can penetrate the skin. Their guidance is to relieve pressure before loosening hydraulic fittings, and to check for pinhole leaks with a piece of cardboard or paper instead of bare hands.
Stored energy in a system is a recognized hazard. OSHA explains that unexpected startup or release of stored energy can cause serious injury during servicing, and that lockout/tagout practices safeguard workers from hazardous energy releases.Â
Follow the machine manufacturer's manual, wear eye and hand protection, and have a qualified technician handle any procedure you are not certain about.
Hydraulic Hose Dash Sizes Explained
Most hydraulic hoses use a dash number: the I.D. in sixteenths of an inch. A 1/2-inch I.D. equals 8/16, so the hose is a -8. A hydraulic hose size calculator or a simple conversion chart will confirm the math.
The SAE J517 hydraulic hose standard is one of the references the industry uses to define common hose types. A few hose types follow a different convention: for SAE 100R5 and 100R14 hose, the dash size matches the equivalent tube O.D., so the sixteenths conversion does not apply. Check the hose type on the layline before assuming the number.
When in doubt, the hydraulic hose manufacturer listed on the layline publishes the size and construction details for that series.
The table below lists common dash sizes and their inside diameters in inches.Â
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Dash Size |
Inside Diameter (Inches) |
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-4 |
1/4 |
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-6 |
3/8 |
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-8 |
1/2 |
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-10 |
5/8 |
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-12 |
3/4 |
|
-16 |
1 |
Because the hydraulic system is built around a specific flow rate, an I.D. that is too small can cause excessive pressure drop, while an I.D. that is too large can reduce system performance and take up more space. Match the original size unless a technician has specified a change.
How to Measure Hydraulic Hose Size Step by Step
Step 1: Measure the Inside Diameter
If the layline is unreadable, use calipers on the cut end of the removed hose and measure across the opening. Convert the result to sixteenths of an inch to get the dash size.
Step 2: Measure the Outside Diameter
The outer diameter (O.D.) does not change the size designation, but it determines whether the hose clears clamps, guards, and bulkhead openings. Measure it with calipers and compare it against the space on the machine.
Step 3: Measure the Overall Length
Measure the overall length from the extreme end of one fitting to the extreme end of the other.Â
For O-ring face seal ends, measure from the sealing face. Hose length can change under pressure, and hose and machine tolerances matter, so allow a small tolerance when comparing against a replacement.
Step 4: Note the Bend and Routing
Record the direction each end points. A hose that fits at the right length can still fail early if it twists or bends sharply once installed. For more on how routing and wear shorten hose life, see this guide to replacing hydraulic hoses in heavy machinery.
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Case 60XT Hose - to Loader Bucket Tilt Cylinders - Rod Ends - #2 |
Case 440 Hose - At Pivot - to Loader Tilt Cylinders - Bore Ends - #2 |
John Deere 120R Hose - MSL - to Loader Lift Cylinders - Rod Ends - 5 |
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Identify the Fitting Ends
The hose I.D. and the fitting size are separate measurements. The fitting has to match the port or mating line it connects to, so measure both ends.
For a male end, measure the outside diameter of the threads with calipers, then find the pitch with a thread pitch gauge. For a female end, measure the inside diameter of the threads.
Common hose fitting styles include JIC 37° flare, O-ring face seal, and tapered pipe thread (NPT/NPTF). JIC fittings seal metal to metal on a 37-degree flared seat, while O-ring face seal fittings use a soft O-ring, so check the seat shape and the sealing method as well as the diameter.
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Pro Tip: Keep the old fittings clean and dry when you compare them against a replacement. Debris in the threads can throw off a measurement. |
Confirm the Pressure Rating and Hose Construction
A replacement hose needs a pressure rating suited to the circuit it serves. The rating is usually printed on the layline of the original hose, and it is also listed on the product page for the replacement. Compare the two.
Product pages for replacement hoses on HW Part Store list a pressure rating and an abrasion-resistant cover where applicable, and some also list the quantity needed per machine, which helps when a repair involves several hoses in the same circuit.
For example, the Case 1825 Hose - to Loader Lift Cylinders is rated at 5500 psi and has an abrasion-resistant cover. The Case 1825 hose page lists two hoses per machine, applies to all serial numbers, and identifies this hose as position #1 on the diagram.Â
Match Your Measurements to the Right Part
Measurements narrow the search, but whether the right hydraulic hose fits on a specific machine depends on the make, model, serial number range, and hose position. Our hose collections are organized by machine and show a diagram with numbered positions.
Each diagram number corresponds to a product page with its listed pressure rating and fit notes. The make and model pages, such as Case aftermarket parts, are a starting point for locating the right machine category.Â
Product pages list the pressure rating, cover, and diagram position, but not every dimension. If you need to confirm your measured I.D., length, or fitting ends, or a hose is not shown for your machine, the support team can help identify the correct part.
Record Your Measurements for Next Time
A hose can fail repeatedly at the same point when the routing and wear points stay the same. Writing down the dash size, length, fitting types, pressure rating, and diagram position for each hose gives you a reference for the next replacement.Â
It also makes it easier to spot patterns, such as a hose that keeps failing at the same bend.
Hose wear and leaks have other causes as well; the guide to the potential causes of hydraulic leaks in heavy machinery covers them.Â
A replacement hose that matches the original size, length, fittings, and pressure rating is more likely to seat, seal, and route as intended. Our guidance on measuring and identifying hoses draws on more than 30 years of hydraulic shop experience.