Speed calculator
Flow to
speed.
Enter bore, rod, flow, and stroke. Get extend and retract speed in inches per second and the full-cycle time — so you know if your pump moves the cylinder fast enough.
Inputs
- Extend speed
- —
- in/sec
- Retract speed
- —
- in/sec
- Extend / retract time
- —
- sec, full stroke
- Full cycle
- —
- sec, out + back
Carries bore, rod, flow, and stroke into the configurator — forces, buckling, and RFQ.
This calculator returns hydraulic cylinder extend and retract speed from flow, bore, and rod, using v = (Q × 231) / (60 × A), plus the full-cycle time for a given stroke. Use it to check whether the pump you have (or plan to buy) moves the cylinder fast enough for the job — and to catch speeds high enough to chew up seals before you commit to a build.
Flow, area, and speed
A cylinder’s speed is nothing more than volume flow rate divided by the area being filled. Oil is measured in gallons per minute; a cylinder cares about cubic inches per second, so the 231 (cubic inches in a gallon) and the 60 (seconds in a minute) are just unit conversions. Fill the full bore area on extend, and the smaller annulus on retract, and you get two different speeds from one flow. Because retract fills less volume per inch of travel, it is always the faster direction on a standard single-rod cylinder — often noticeably so with a large rod.
Worked example: a 4-inch bore with a 2-inch rod fed 10 GPM. Bore area is 12.57 in², so extend speed is (10 × 231) / (60 × 12.57) ≈ 3.1 in/sec. The annulus is 9.42 in², so retract speed is about 4.1 in/sec. A 24-inch stroke therefore takes roughly 7.8 seconds out and 5.9 seconds back. Double the flow and both speeds double — flow and speed are directly proportional, which makes this an easy number to tune by adjusting the pump or a flow control.
When speed becomes a problem
Faster is not always better. Standard hydraulic rod and piston seals are generally rated to around 24 inches per second; run past that and seal wear accelerates, heat builds, and cushioning becomes essential to keep the piston from slamming the end caps. If your numbers push into that range, it is a design conversation — special seals, cushions, or a deliberately throttled flow. Speed also interacts with everything else: high flow into a small bore spikes velocity, while a big bore quietly demands far more flow than people expect to hit a modest speed. Configure the full cylinder and we flag the speed limit for you.
Related tools
- Get the force behind the motion with the force calculator.
- Make sure the rod survives the load with the rod buckling calculator.
Cylinder speed FAQ
How do you calculate hydraulic cylinder speed from flow?
Speed equals flow divided by area, converted to consistent units: v = (Q × 231) / (60 × A). Q is flow in GPM, 231 is cubic inches per gallon, 60 converts minutes to seconds, and A is the working area in square inches. A 4-inch bore at 10 GPM extends at about 3.1 in/sec.
Why does a cylinder retract faster than it extends?
On retract, the rod fills part of the bore, so the same flow only has to fill the smaller annulus area — less volume per inch of travel means more inches per second. The bigger the rod relative to the bore, the larger the speed difference between extend and retract.
How much flow do I need for a target speed?
Rearrange the formula: Q = (v × 60 × A) / 231. Pick your target extend speed in in/sec, multiply by the bore area, and you get the GPM the pump must deliver at the cylinder. Remember that hose and valve losses mean flow at the cylinder is lower than flow at the pump.
Is there a maximum safe cylinder speed?
Seal manufacturers typically cap piston speed around 24 in/sec for standard hydraulic seals; past that, seals wear fast and heat builds. High-speed applications need cushions, special seals, or a flow review. WestCraft flags this automatically when you configure a cylinder.