Gear Ratio Calculator

Try this simulation yourself

Start with the default — Z₁ = 20 teeth (driver) and Z₂ = 40 teeth (driven). The gear ratio reads 2.00:1. Hit Play Animation and watch the small blue gear spin twice for every one rotation of the large red gear. That's the gear ratio — visible, not memorized.

Drag the Z₂ slider up to 60 — the driven gear grows larger, ratio jumps to 3:1. Output RPM drops to 333 while output torque triples. Look at the speed and torque comparison bars at the top — the tradeoff is instant and obvious.

Now flip it — set Z₁ = 40 and Z₂ = 20. Ratio becomes 0.50:1. The info bar switches to "Speed ↑ Torque ↓ (Overdrive)." Output spins twice as fast but with half the torque. This is what top gear in a car does.

Set Z₁ = Z₂ = 30 — ratio is exactly 1:1. Direct drive. Same speed, same torque. The info bar says "Speed = Torque = (Direct)." Both gears are the same size and spin at the same rate.

Drag the Input RPM slider to 3000 — watch the output RPM change proportionally. At 2:1 ratio, output stays locked at 1500 RPM no matter how you adjust input speed. The ratio holds.

Increase Input Torque to 200 Nm — output torque jumps to 400 Nm at 2:1 ratio. The purple torque bar doubles in length. This is mechanical advantage — you're trading speed for force.

Use the speed button (0.5×, 1×, 2×, 4×) to slow down or speed up the animation. At 0.5× you can count individual teeth meshing at the contact point.