How do I calculate the gear ratio I need?

Required ratio = motor RPM ÷ target wheel RPM, where wheel RPM = (speed × 60) ÷ (π × wheel diameter). A 6000 RPM motor driving 80 mm wheels at 1 m/s needs roughly a 25:1 reduction.

Does gearing increase torque?

Yes — output torque is multiplied by the gear ratio, minus friction losses. A 10:1 gearbox at 90% efficiency turns 0.1 N·m of motor torque into about 0.9 N·m at the output, while dividing speed by 10.

What gear ratio efficiency should I assume?

Roughly 90–95% per spur stage, 80–90% for planetary gearboxes overall, 70–90% for belts, and only 30–70% for worm gears. Multi-stage gearboxes multiply these losses.

Gear Ratio Calculator for Robots — Speed & Torque

How this calculator works

Wheel RPM = (speed × 60) ÷ (π × wheel diameter)
Required ratio = motor RPM ÷ wheel RPM
Output torque = motor torque × ratio × efficiency

Gearing trades speed for torque at a fixed exchange rate: divide speed by N, multiply torque by N (minus friction). That's why a tiny 6000 RPM motor behind a 30:1 gearbox can out-pull a much larger direct-drive motor.

Ratio too big for one stage? Single spur stages are practical up to about 5:1. Above that, stack stages (two 5:1 stages = 25:1) or use a planetary gearbox — that's exactly what's inside off-the-shelf gearmotors.

Not sure your motor torque is enough even after gearing? Run the Motor Sizing Calculator first to find the torque your robot needs at the wheel, then use this tool to check your motor + ratio combination reaches it.

Common questions

Should I gear for top speed or torque?

Gearing for a speed you'll never safely use costs you acceleration and hill-climbing everywhere else. Pick the ratio for your realistic operating speed; the torque multiplication comes free.

Why use 80% of free-run RPM?

Motor datasheets quote no-load speed. Under real load a healthy DC motor runs at roughly 75–85% of that; using 80% keeps the estimate honest.

Parts this calculation leads to

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Gearmotors

Motors with the ratio already built in — the easy path.

Browse gearmotors →

Gear Sets

Spur gear assortments and pinions for custom gearboxes.

Browse gear sets →

Timing Belts & Pulleys

GT2 belts and pulleys for quiet, clean reductions.

Browse belts & pulleys →

Bearings & Shafts

Support shafts properly or your gears won't mesh for long.

Browse bearings →