Gearbox Ratio, Speed & Torque Calculator
Three tools for sizing and cross-referencing speed reducers and gearmotors — ratio and output speed, output torque, and service-factor sizing. Formulas shown below.
How these are calculated
| Result | Formula |
|---|---|
| Gear ratio | ratio = input RPM ÷ output RPM |
| Output speed | output RPM = input RPM ÷ ratio |
| Input torque | T in (lb-in) = 63,025 × HP ÷ RPM (= 5,252 × HP ÷ RPM in lb-ft) |
| Output torque | T out = T in × ratio × efficiency |
| Design rating | required HP = motor HP × service factor |
Constants and relationships are standard power-transmission engineering (the 63,025 lb-in and 5,252 lb-ft horsepower-torque constants; torque multiplication by gear ratio). Service-factor practice follows AGMA and individual gearbox manufacturers' rating tables — use their published factor for your duty. Efficiency ranges reflect typical worm vs. helical reducer performance; use your unit's rated efficiency for a precise result.
Frequently asked questions
How do you calculate gear ratio?
Gear ratio equals the input speed divided by the output speed. If a motor turns the input at 1,750 RPM and the output shaft turns at 58 RPM, the ratio is 1,750 ÷ 58, or about 30:1.
How do you find output RPM from a gear ratio?
Divide the input RPM by the ratio. A 1,750 RPM motor through a 30:1 reducer gives an output of about 58 RPM.
How does a gearbox change torque?
A speed reducer multiplies torque by roughly the gear ratio while dividing speed by the same ratio. Efficiency losses reduce the output slightly: output torque = input torque × ratio × efficiency.
What is service factor on a gearbox?
Service factor is a multiplier for shock and duty. Multiply the motor horsepower by the service factor to get the required design rating, then choose a gearbox whose rated capacity meets or exceeds it. Manufacturers publish service factors by application and hours per day.
Are worm gearboxes less efficient than helical?
Yes. Worm gear reducers are typically 60 to 80 percent efficient depending on ratio, while helical reducers are often 95 percent or higher. Lower efficiency reduces output torque and generates more heat, so it matters when sizing.
Can Jealco supply a replacement gearbox or gearmotor?
Yes. As an independent distributor, Jealco cross-references and sources gearboxes, speed reducers, and gearmotors across manufacturers. Send the nameplate details — manufacturer, model, ratio, input HP/RPM, output RPM, mounting, and shaft size — for a replacement quote.