Jackshaft Ratio Calculator
Calculate compound gear ratios through intermediate jackshafts. Enter sprocket or gear teeth for each stage, see the overall ratio, output RPM, and torque multiplication — with an interactive multi-stage drive chain visualizer.
What is a Jackshaft System?
A jackshaft (countershaft or layshaft) is an intermediate rotating shaft that sits between a motor and the final driven shaft. It carries two or more gears or sprockets — one receives power from the input side, and the other transmits power to the output side. By using different-sized sprockets on the jackshaft, you create a compound gear ratio that multiplies the reduction achieved by each individual stage.
For example, a go-kart engine spinning at 3,600 RPM with a Stage 1 ratio of 3:1 and a Stage 2 ratio of 4:1 produces an overall compound ratio of 12:1. The axle turns at 3,600 ÷ 12 = 300 RPM, with torque multiplied by roughly 12× (minus friction). This is why jackshafts are essential in applications requiring high torque from small, high-speed motors.
Formulas & Equations Used
This Jackshaft Ratio Calculator uses the following core equations:
1Single Stage Gear Ratio▼
A 10-tooth driver meshing with a 30-tooth driven gear: Ratio = 30 ÷ 10 = 3:1. The output turns 3× slower with 3× more torque.
2Compound Ratio (Overall)▼
Stage 1 = 3:1, Stage 2 = 4:1 → Overall = 3 × 4 = 12:1. Each stage's ratio multiplies into the total.
3Output RPM▼
Motor at 3,600 RPM through 12:1 ratio: Output = 3,600 ÷ 12 = 300 RPM.
4Output Torque▼
10 Nm input × 12:1 ratio × 0.95 efficiency = 114 Nm output. Expect ~2-5% loss per stage from friction.
How to Use This Jackshaft Ratio Calculator
Follow these 3 simple steps:
Enter Stage 1 Teeth
Enter the number of teeth on the driver and driven sprocket/gear for Stage 1 (motor to jackshaft).
Enter Stage 2 Teeth
Enter the driver and driven teeth for Stage 2 (jackshaft to output axle). Add more stages if your system requires them.
Get Results
View the individual stage ratios, compound overall ratio, output RPM for any input speed, and estimated torque at the output shaft.
Example Problems & Step-by-Step Solutions
Here are 3 worked examples using this Jackshaft Ratio Calculator:
Example 1Go-kart: 10T→30T on jackshaft, then 12T→48T to axle
Example 2CNC spindle: 20T→60T, then 15T→45T (two jackshafts)
Example 3Conveyor: need 60 RPM output from 1,750 RPM motor
RPM & Torque Calculator
Enter your motor's RPM and torque to see the output values through your jackshaft system. The compound ratio from the hero calculator is applied automatically.
Frequently Asked Questions
What is a jackshaft?▼
A jackshaft (countershaft or layshaft) is an intermediate shaft in a multi-stage drive system. It sits between the motor and final driven shaft, carrying one or more gears/sprockets to achieve a compound gear ratio. This allows high ratios in a compact package.
How do you calculate compound gear ratio with a jackshaft?▼
Multiply the individual stage ratios together. If Stage 1 has a 3:1 ratio and Stage 2 has a 4:1 ratio, the overall compound ratio is 3 × 4 = 12:1. The output shaft turns once for every 12 turns of the input shaft.
Why use a jackshaft instead of a single large gear reduction?▼
A jackshaft allows high gear ratios in a compact, lightweight package. A single-stage 20:1 ratio needs a very large driven gear. Two stages of 5:1 and 4:1 achieve the same 20:1 with much smaller gears, less weight, better efficiency, and lower cost.
What are common jackshaft applications?▼
Go-karts, mini bikes, CNC machines, conveyor belt drives, industrial mixers, printing presses, lathe gearboxes, and agricultural equipment. Any application needing high torque multiplication or precise speed reduction benefits from jackshaft systems.
How does a jackshaft affect torque?▼
Torque multiplies by the overall gear ratio minus friction losses of ~2-5% per stage. A 10 Nm motor through a 12:1 jackshaft system delivers approximately 114 Nm at the output (at 95% efficiency per stage: 10 × 12 × 0.95² ≈ 108 Nm).