Hydraulic cylinder stroke is the distance the rod travels from fully retracted to fully extended. To measure it, you subtract the retracted pin-to-pin length from the extended pin-to-pin length. The process is straightforward with a working cylinder and a tape measure, but gets trickier when the cylinder is seized, still mounted on a machine, or you need tight accuracy for a replacement order.
The Basic Measurement Method
Every hydraulic cylinder has two connection points, one at each end. On pin-mounted cylinders, these are the clevis or trunnion pins. The measurement process works in two steps:
- Retracted length (closed centers): Fully retract the cylinder rod. Measure from the center of the pin at one end to the center of the pin at the opposite end.
- Extended length (open centers): Fully extend the rod. Measure center-to-center on the same two pins.
Stroke length equals the extended measurement minus the retracted measurement. If your cylinder measures 40 inches extended and 24 inches retracted, the stroke is 16 inches.
Where to Measure on Different Mounting Styles
The pin-to-pin method works cleanly on clevis-mounted cylinders, where each end has a U-shaped bracket with a visible pin. But not every cylinder mounts this way, and the mounting style changes where you take your reference points.
Trunnion-mounted cylinders pivot on pins located partway along the barrel rather than at the ends. Your measurement still runs from the center of the trunnion pin to the center of the rod-end pin, but the trunnion’s position along the barrel means the retracted length will be different than what you’d expect from looking at the cylinder’s overall size.
Flange-mounted cylinders bolt flat against a surface at either the head or cap end. There’s no pin at the flange end, so you measure from the flange mounting face to the center of the rod-end connection point. If the rod end also uses a flange or threaded attachment instead of a pin, measure to whatever surface mates with the machine. The key is consistency: use the same two reference points for both your retracted and extended measurements, so the subtraction gives you pure rod travel.
Tools You’ll Need
For most field measurements, a steel tape measure is sufficient. You’re measuring overall lengths that are typically between one and several feet, and a tape gets you within a millimeter if you’re careful about finding the true center of each pin.
If you need bore diameter (the inside width of the cylinder tube) for ordering a replacement, a set of calipers works for smaller cylinders. For precision bore checks, an internal micrometer taken at two planes 90 degrees apart will reveal whether the tube has worn oval. On cylinders longer than arm’s length, repair shops use a specialized bore gauge: a T-shaped device with two wheels on one side, a spring-loaded measuring pin on the other, and extension pieces that reach deep into the tube. A dial indicator on the gauge displays changes in bore diameter as you slide it through.
For stroke length specifically, though, the tape measure does the job. Just make sure you’re measuring to pin centers, not to the outer edges of the mounting hardware.
Measuring a Seized or Broken Cylinder
A cylinder that won’t extend fully is the most common complication. If the rod is stuck partway, you can measure the visible portion of the rod protruding from the gland (the housing where the rod exits the barrel), then estimate or calculate how much rod remains inside. This usually requires referencing the manufacturer’s specifications or a parts diagram for that cylinder model, since there’s no way to directly see the internal length without disassembly.
If the cylinder is completely seized in the retracted position, the rod may not be visible at all. In that case, your best option is to find the model number stamped on the barrel or end cap and look up the stroke from the manufacturer’s catalog. Most manufacturers engrave or stamp the bore diameter and stroke length directly on the cylinder body, often on a nameplate or rolled into the barrel surface. A reading like “3.5 x 16” typically means 3.5-inch bore and 16-inch stroke.
Safety Before You Start
Hydraulic systems store energy even when the machine is off. A cylinder under residual pressure can extend or retract unexpectedly when fittings are loosened or hoses disconnected, and a moving rod can crush fingers or worse. OSHA’s lockout/tagout standard (29 CFR 1910.147) requires that stored hydraulic energy be isolated and controlled before any servicing or maintenance work begins.
In practical terms, this means shutting down the hydraulic power unit, relieving system pressure by cycling the control valve with the pump off, and mechanically securing the load so it can’t shift if the cylinder moves. If the cylinder is supporting any weight (a raised boom, a press platen, a suspended platform), block or crib the load before you put your hands or a tape measure near the rod.
How Accurate Your Measurement Needs to Be
For ordering a replacement cylinder, your stroke measurement needs to be within about 2mm for general industrial applications. Tighter applications demand more care. Assembly line cylinders that align parts for welding or fastening typically need tolerances of ±0.5mm or better. Precision manufacturing equipment may require ±0.1mm, and metrology-grade systems work within ±0.02mm.
If your measurement is off by even a few millimeters on a critical application, the consequences are real. A cylinder that’s too short won’t reach full travel, and one that’s too long can bottom out and damage the end caps or connected equipment. For general-purpose cylinders on loaders, splitters, or farm equipment, being within an eighth of an inch is usually fine. For anything involving automated positioning, measure twice and confirm against the manufacturer’s spec sheet before ordering.
Other Dimensions to Record
While you have the cylinder accessible, capture the other measurements you’ll need if you’re ordering a replacement or rebuild kit. Bore diameter is the inside width of the cylinder barrel. Rod diameter is the width of the chrome shaft. Measure both with calipers if possible, or use a tape wrapped around the rod’s circumference and divide by pi (3.14) to get the diameter. Note the mounting style, pinhole diameters at both ends, and the distance between any port locations on the barrel. Recording everything at once saves you from having to go back out and re-measure when the supplier asks for dimensions you didn’t think to capture.