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Winding Torque Calculator
Calculate the roll torque required to hold a stated web tension at the current diameter.
What this calculator solves
Center-driven rewinds and unwinds must change torque as diameter changes to preserve tension. This tool translates a known force and measured diameter into the torque present at the roll.
Inputs and units
Total tension is in newtons. Diameter is the wound outside diameter at the current instant; the formula converts it to metres of radius. Efficiency represents gearing, belt or coupling losses and must come from the drive specification or commissioning data.
Calculation method
Roll torque = tension × radius. Drive-side demand = roll torque ÷ efficiency. Constant torque cannot maintain constant tension as a roll builds or unwinds because the radius changes.
Worked production example
A 600 mm roll running at 200 N needs 60 N·m at the roll. With a 90% efficient drive path, the nominal upstream requirement is 66.67 N·m before acceleration and friction allowances.
How to use the result
Compare the result at core and full roll, then verify the controller's scaling and gearbox ratio. Use the Winder Acceleration Torque tool when ramp torque also matters.
Common production mistakes
Do not enter diameter where radius is expected in a manual worksheet, or tension per width where total force is required. Do not treat the efficiency-adjusted number as a complete motor sizing result.
Assumptions and limitations
The result is steady-state tension torque. Bearing drag, inertia, safety factor, gearbox service factor, regenerative braking and control-loop dynamics are excluded.
Related workflow and sources
Rockwell Automation and Montalvo state the same force-times-radius relationship for center-driven winders. Rockwell drive calculation reference. Last reviewed: 2026-08-27.