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⚙️ Gear Ratio Calculator

Enter the driver (input) and driven (output) gear teeth counts and input RPM to instantly calculate gear ratio, output RPM, and torque multiplier. Supports an optional 2-stage gear configuration.

Enter the gear teeth counts and input RPM. Real gear trains lose some efficiency to friction (this is an ideal calculation).

Results
Gear Ratio
—
Output RPM
—
Torque Multiplier
—
GUIDE

Learn more

01

What Is Gear Ratio?

Gear ratio describes how rotational speed (RPM) and torque change when two gears mesh.

Gear ratio = driven gear teeth ÷ driver gear teeth

A ratio greater than 1 means reduction (lower output RPM, higher torque); a ratio less than 1 means overdrive (higher output RPM, lower torque).
02

Calculating Output RPM and Torque Multiplier

Output RPM = Input RPM × (driver teeth ÷ driven teeth)
Torque multiplier = driven teeth ÷ driver teeth (ideal case, no friction losses)

For example, with 10 driver teeth and 40 driven teeth, the gear ratio is 4:1; at 1000 RPM input, output is 250 RPM with 4× torque. In practice, bearing friction and mesh losses mean transmission efficiency is below 100%, so real output torque is somewhat lower than this calculated value.
03

Overall Ratio for a 2-Stage Gear Train

With a 2-stage configuration (e.g. an idler stage inside a reducer), multiply each stage's ratio to get the overall ratio.

Overall ratio = stage 1 ratio × stage 2 ratio

If stage 1 is 4:1 and stage 2 is 3:1, the overall ratio is 12:1 — reducing input RPM to 1/12 while multiplying torque by 12×. Multi-stage reducers let you achieve large reduction ratios in a compact space.

Frequently asked questions

Can I use gear diameter instead of teeth count?
Yes — if the gears share the same module (pitch), the teeth-count ratio equals the pitch-diameter ratio, so diameters give the same result. Gears with different modules must use teeth counts instead.
How far off is the torque multiplier from real-world values?
This calculator assumes an ideal (100% efficient, frictionless) case. Real gear trains typically run at 90–98% efficiency, so actual output torque is closer to the calculated value times that efficiency.
Can I see the intermediate RPM in a 2-stage setup?
This calculator shows the final output RPM and overall ratio/torque multiplier. To get the intermediate RPM (right after stage 1), multiply the input RPM by the reciprocal of stage 1's ratio yourself.