Gear, RPM & drivetrain calculators
Choose a calculator by task. GIIRR keeps each tool focused so the inputs, formula and limitations stay clear.
Gears
Gear Ratio Calculator
Use tooth counts from a simple gear pair to see the reduction or overdrive ratio, output shaft speed and torque multiplication.
Open calculator →GearsCompound Gear Train Calculator
Multiply several gear-pair ratios to get a compound gear train’s overall ratio and output speed.
Open calculator →GearsTorque After Gear Ratio Calculator
Estimate idealized torque multiplication after a reduction or overdrive ratio.
Open calculator →Drivetrain
RPM to Speed Calculator
Estimate vehicle speed at a given engine RPM from the selected gear, differential ratio and rolling diameter.
Open calculator →DrivetrainSpeed to RPM Calculator
Work backward from road speed to engine RPM, useful when comparing highway gearing, tire sizes or differential changes.
Open calculator →DrivetrainFinal Drive Calculator
See the overall reduction between engine and wheels for one transmission gear and differential/final-drive combination.
Open calculator →DrivetrainMulti-Gear Speed Calculator
Paste a list of gear ratios and see a complete speed-by-gear table at one engine RPM.
Open calculator →Chain drive
Bicycle
Bicycle Gear Ratio Calculator
Compare chainring and cassette combinations by their simple mechanical ratio.
Open calculator →BicycleGear Inches Calculator
Express bicycle gearing as an equivalent direct-drive wheel diameter, useful for comparing setups across wheel sizes.
Open calculator →BicycleCycling Cadence to Speed Calculator
Estimate bike speed from cadence and gearing without needing a power model.
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