Which gear is the driver?
The driver is the powered gear; the driven gear receives motion.
Gear Ratio Calculator
Find gear ratio from tooth counts or speeds, then estimate output RPM and torque.
Calculate a gear ratio
Use teeth or RPM to get the ratio, and optionally enter input torque for output torque.
About this calculator
How to use Gear Ratio Calculator, plus the formulas and logic behind the results.
Tool description
The Gear Ratio Calculator computes reduction/overdrive ratio from teeth or speeds and can estimate output speed and torque for a single gear stage.
How to use
- Choose teeth or RPM mode.
- Enter driven/driver teeth or input/output RPM.
- Optionally enter input torque and efficiency.
- Select Calculate to view ratio and related outputs.
Formulas & reference
i = N_driven ÷ N_driveri = n_in ÷ n_outn_out = n_in ÷ iτ_out ≈ τ_in × i × (η ÷ 100)
Gear basics
- Ratio = driven ÷ driver (teeth)
- Ratio = input RPM ÷ output RPM
- Output RPM = input RPM ÷ ratio
- Output torque ≈ input torque × ratio × η
Calculation logic
Ratio is driven/driver or input/output speed. If input RPM is known (RPM mode provides both speeds; teeth mode can still show ratio only unless input torque is used), torque out scales by ratio and efficiency.
Simple spur-gear model. Compound trains multiply stage ratios. Efficiency is an estimate you provide.
Gear Ratio Calculator FAQ
Common questions about this calculator and how to use the results.
What does a ratio of 3:1 mean?
The output turns once for every three input turns (speed down, torque up).
Can ratio be less than 1?
Yes—that is overdrive (output faster than input).
Are worm gears supported?
You can enter an effective ratio, but worm efficiency is often much lower.
Why enter efficiency?
Real meshes lose power; torque out is reduced by η.
Do belt pulleys work the same way?
Yes for ideal pitch diameters/teeth equivalents.