Use this engineering calculation for a transparent preliminary estimate or independent arithmetic check when geometry, materials, loads, operating conditions, and units are defined consistently.

Driver Diameter Millimeters (mm)

Required number input.

Driven Diameter Millimeters (mm)

Required number input.

Ideal no-slip driven-to-driver pulley speed ratio from pitch diameters. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Speed Ratio

The resulting speed ratio returned as a number.

• Ideal speed and pitch relationships do not include slip, tooth or belt geometry limits, center distance, wrap, tension, efficiency, wear, vibration, service factors, or strength. Manufacturer selection procedures remain necessary.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check assumptions against drawings, measurements, current material data, and the applicable design code. Apply required load combinations and safety factors, then obtain qualified review and testing for consequential designs.

• Chain Drive Speed Ratio

  Ideal driven-to-driver chain sprocket speed ratio from integer tooth counts.

• Gear Ratio

  Ideal simple external-gear speed reduction ratio from driven and driver tooth counts; excludes idlers and losses.

• Pulley Belt Length Open

  Approximate open-belt pitch length 2C+π(D+d)/2+(D−d)²/(4C) for center distance C.