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See rotation through gears and pulleys

Switch between external gears and an open belt to inspect speed ratios and rotation direction.

Diagram and inputs ↓

Choose another visualization (19 topics)

Start with a familiar scene

Turn different-sized gears and pulleys, as in a transmission.

Choose an example to update the diagram and calculation below.

More numeric references and examples

Start with a reference or example

Get a sense of the value, then inspect the diagram or motion.

Reference / example	Value	What it means
Gear reduction	20 → 40	30 rpm input → 15 rpm output; opposite direction
Gear speed increase	40 → 20	30 rpm input → 60 rpm output; opposite direction
Pulley example	20 → 40 mm	30 rpm input → 15 rpm output; same direction

Assumes matching gear modules or no belt slip. Pulley dimensions are effective/pitch diameters.

Applies to condition A. Then press Play or Reveal.

Visual preview

Ready

2D · front view of gears / pulleys

Playback speed

0.00 sElapsed time

Tooth outlines are approximate illustrations. Assumes a no-slip belt and backlash-free external gears. This is not a tooth, strength or belt-tension design tool.

Enter your own values (open here)

Conditions

Input unit

Enter integer tooth counts for gears or belt pitch/effective diameters for pulleys.

How to read this view

Ratio and direction

Output rpm=input rpm×driver teeth/driven teeth. External gears rotate oppositely; an open belt rotates in the same direction. For pulleys, use effective diameters instead of teeth.

High-speed display

Choose slow playback when the fastest displayed wheel exceeds 120 rpm. Follow the highlighted marker rather than apparent tooth flicker.

From rotation speed to gear motion

1. Match the unitsRotational speed converter →
2. Calculate with the required inputsGear speed ratio and torque →
3. See the motion or differenceGear and pulley rotationCurrent page

Supply tooth counts, input speed and torque as required. Identify the input and output sides.

Each tool opens with its own conditions. Values are not transferred automatically.