ganak.appGear Ratio Calculator
Free gear ratio calculator. Find gear ratio from tooth counts, calculate RPM and output speed, compute vehicle speed from drivetrain specs, and analyze bicycle gearing with gear inches and development.
20T driving · 40T driven · Speed Reduction
Gear Details
Ratio, torque, speed, and direction at a glance
What is a Gear Ratio Calculator?
Understand gear ratios and why they matter
A gear ratio calculator determines the relationship between the number of teeth on two meshing gears. The gear ratio equals Driven Teeth ÷ Driving Teeth — a ratio of 3:1 means the driving gear must turn three times for each revolution of the driven gear, tripling output torque at the cost of speed. This tool covers simple spur gears, compound gear trains, automotive drivetrains, and bicycle gearing.
Torque & Speed
Calculate torque multiplier and output speed from tooth counts
Vehicle Speed
Find vehicle speed from engine RPM, gear ratios, and tire size
Bicycle Gearing
Gear inches, development, and speed at every cadence
How Gear Ratio is Calculated
The formulas behind every calculation mode
Basic Gear Ratio
Gear Ratio = Driven Teeth ÷ Driving Teeth
Output RPM
Output RPM = Input RPM ÷ Gear Ratio
Vehicle Speed
Speed (mph) = (RPM × π × Tire Diameter) ÷ (Overall Ratio × 1056)
Compound Ratio
Overall = Stage 1 Ratio × Stage 2 Ratio
Bicycle Gearing Formulas
Gear Inches = (Chainring ÷ Cog) × Wheel Diameter (in)
Development (m) = Gear Ratio × Wheel Circumference (m)
Gain Ratio = Development ÷ (2π × Crank Length)
Real-World Gear Ratio Examples
Common applications across industries
Automotive 1st Gear
A typical first gear ratio of 3.5:1 with a 3.73 final drive gives an overall ratio of 13.06:1 — maximum torque for acceleration.
Road Bike Climbing
A 34T chainring with a 28T cog gives 1.21:1 — a low gear ratio (about 33 gear inches) ideal for steep climbs.
Industrial Reducer
A two-stage worm gear reducer with 50:1 per stage provides 2500:1 overall ratio — extreme torque for heavy machinery.
Go-Kart Sprocket
An 11T driver with a 60T rear sprocket gives 5.45:1 — balancing top speed with acceleration for karting.
Common Gear Ratio Mistakes
Avoid these frequent errors
Swapping driving and driven gears
The driving gear is the input (connected to the motor/pedals). The driven gear is the output. Swapping them inverts the ratio.
Ignoring direction reversal
External spur gears reverse rotation direction. If you need same-direction output, add an idler gear (which does not change the ratio).
Forgetting the final drive ratio
For vehicle speed calculations, the overall ratio = transmission ratio × final drive (axle) ratio. Omitting the final drive gives incorrect speed.
Confusing gear ratio with speed ratio
Gear ratio = driven/driving teeth (output torque multiplier). Speed ratio is its inverse (output speed / input speed).
Frequently Asked Questions
Common questions about gear ratios, RPM, vehicle speed, and bicycle gearing