Car and Motorcycle Gear Ratio RPM Speed Calculator

Calculate vehicle speed by gear from engine RPM, primary drive, final drive, gear ratios, and wheel diameter for cars and motorcycles.

Drivetrain speed ladder

See speed in every gear at your RPM, then check engine RPM at a target speed. Change the ratios to compare a setup.

Vehicle profile Car
Units
Transmission gear ratios Enter numerical ratios such as 3.20:1
Engine Gearbox Wheel
Live drivetrain model Live: change RPM or ratios and watch the drivetrain react.

Educational estimate only. Use measured vehicle data and manufacturer specifications for decisions about a real vehicle.

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Frequently Asked Questions

How is speed calculated from a gear ratio?

The calculator divides engine RPM by the primary, selected gear, and final drive ratios to estimate wheel RPM. It then multiplies wheel RPM by the wheel circumference and converts the result to km/h or mph.

What is the difference between a gear ratio and the overall ratio?

The gear ratio describes one transmission gear. The overall ratio combines the primary drive, selected gear, and final drive, so it represents the full reduction between the engine and the wheel.

Why does a lower numerical gear ratio produce more speed?

A lower numerical ratio reduces the number of engine revolutions needed for one wheel revolution. At the same engine RPM and wheel size, that lets the wheel turn faster and produces a higher theoretical vehicle speed.

Does this calculator predict real road speed exactly?

No. It is a kinematic estimate. Tire growth, clutch or torque converter slip, drivetrain losses, tire load, rolling circumference, speedometer error, and road conditions can move real speed away from the calculated value.

# How the Drivetrain Turns RPM Into Speed

A drivetrain does not send engine RPM directly to the road. The primary drive, selected transmission gear, and final drive reduce engine rotation before it reaches the wheel. The wheel circumference then turns that rotation into a theoretical road speed.
3 ratios Primary, gear, final drive
6 gears Editable speed ladder
2 systems Metric and Imperial

# The Formula Behind the Result

Overall ratio equals primary drive multiplied by the selected gear ratio and final drive ratio. Wheel RPM equals engine RPM divided by that overall ratio. Speed then equals wheel RPM multiplied by wheel circumference, with the final unit conversion to km/h or mph.
Input Changes Interpretation
Engine RPMEvery gear speedMore engine rotation produces more theoretical speed
Gear ratioOne row in the ladderA larger number gives more reduction and less speed
Final driveEvery gear speedA larger number increases reduction across the whole box
Wheel diameterEvery gear speedA larger circumference travels farther per wheel revolution

# How to Read the Speed Ladder

The speed column answers how fast the vehicle would travel at the entered engine RPM in each gear. The RPM column answers the reverse question at your target speed. Use both views to spot the practical handoff between gears and to see whether a target speed asks for more RPM than the entered redline.
Use Real Rolling Circumference When It Matters
A sidewall size or nominal wheel diameter is only an approximation. Tire pressure, load, wear, construction, and tire growth change the rolling circumference. Replace the preset diameter with a measured value when you need a closer estimate.

# Cars and Motorcycles Share the Physics

The same ratio and circumference relationship works for cars, motorcycles, and other wheeled vehicles. The presets only give you a sensible starting point. They do not identify a specific model, account for automatic transmission slip, or certify the speed shown on a dashboard.

Bibliographic References

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