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Why I Wrote The Sheet Mechanic (And Why Calculations Aren’t Enough)

For engineers who already know the math—but still lose projects. For the last few years, I’ve been sharing technical guides here on Mechanical Design Handbook —how to size a motor, how to calculate fits, and (as you recently read) how to choose between timing belts and ball screws. But after 25 years in industrial automation, I realized something uncomfortable: Projects rarely fail because the math was wrong. They fail because: The client changed the scope three times in one week. A critical vendor lied about a shipping date (and no one verified it). The installation technician couldn’t fit a wrench into the gap we designed. University taught us the physics. It didn’t teach us the reality. That gap is why I wrote my new book, The Sheet Mechanic . This is not a textbook. It is a field manual for the messy, political, and chaotic space between the CAD model and the factory floor. It captures the systems I’ve used to survive industrial projec...
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Pneumatic Cylinder Calculator

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Tool · Pneumatics · ISO 15552

Size a pneumatic cylinder in your browser. Get push and pull force, load ratio for a lifted or sliding load, free air per cycle and per minute including the tubing, peak flow for valve sizing, and kinetic energy for the cushion. Compare every ISO 15552 bore at your pressure, watch the cylinder stroke, and print the result to PDF.

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Extending
Rod position-
Force-
Air this cycle-
Air per minute-

Inputs

Cylinder

Pick an ISO 15552 bore to fill in its standard rod, or choose Custom. Use the pressure at the cylinder, after the regulator and the valve.

Duty and tubing

Leave retract time blank to estimate it from the extend time at the same flow setting: with meter-out control the retract stroke is slower (it must exhaust the larger cap side), with meter-in it is faster (it fills the smaller rod side). Tubing between the valve and the cylinder is filled and vented on every stroke, so it counts toward air use.

Load (optional)

Load ratio is the force the load needs divided by the theoretical cylinder force. Cylinder makers publish a recommended limit and an allowable cushion energy for each series; enter them from your maker's catalog.

Results update as you type. Copy link saves this exact cylinder in the URL.

Forces, air and speed

Extend vs retract

Checks

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    Charts

    Force vs pressure

    Push force by ISO 15552 bore

    ISO 15552 bore comparison

    Same pressure, stroke, duty and tubing for every bore. Click a row to select that bore.

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    Equations, assumptions and limits

    Force

    Fpush = p · πD2/4    Fpull = p · π(D2 − d2)/4

    p is gauge pressure, D the bore and d the rod diameter. These are theoretical forces without seal friction. For a single acting cylinder the full spring force is subtracted from the push force, and the retract force is the spring force.

    Air consumption

    Vfree = A · s · (p + patm)/patm + Vtube · p/patm
    • Boyle's law at constant temperature, referred to free air at patm = 1.01325 bar (standard atmosphere). The swept volume starts at zero size and ends full at absolute pressure; the tubing starts at atmospheric pressure, so it only needs the gauge part.
    • Air per minute = (extend + retract air) × cycles per minute × number of cylinders.
    • Retract force is smaller because the rod covers part of the piston: Fpull/Fpush = A2/A1 = 1 − (d/D)2.
    • Speed at the same flow setting, ignoring load and air compressibility: with meter-out control the exhausting chamber empties at equal flow, so vretract/vextend = A2/A1 (retract slower); with meter-in or a supply-limited valve the driving chamber fills at equal flow, so vretract/vextend = A1/A2 (retract faster). Real cylinders deviate with load, friction and valve size; enter measured times when you have them.
    • Peak flow uses the average stroke speed s/t. Size the valve and the supply for this flow, with margin for the acceleration at the start of the stroke.

    Load and energy

    • Required force: m·g for a vertical lift, μ·m·g for horizontal sliding, with g = 9.80665 m/s2. Load ratio = required force / theoretical force.
    • Kinetic energy ½mv2 uses the average stroke speed. If the piston speeds up through the stroke, the speed at the end cushion is higher than the average, so the real energy is higher. Treat this value as a lower bound.

    ISO 15552 sizes

    Bores and standard rod diameters: Ø32 to Ø125 from the SMC C96 (ISO 15552) catalog; Ø160 to Ø320 derived from the Festo DSBG (ISO 15552) catalog forces at 6 bar. Check the rod size of your chosen series; some makers offer other rods.

    Validity

    Static force and average speed only. Not included: seal friction, pressure drop in the valve and tubing, acceleration of the load, side load and rod buckling, temperature change during fast strokes, and the maker's own speed and cushion limits.

    Checked in code against the SMC C96 theoretical output table (all bores, 0.5 MPa) and the Festo DSBG theoretical forces at 6 bar (Ø160 to Ø320), and against an independent mass balance for the free air.

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