Auto Tools

Gear Speed Calculator

Estimate vehicle speed from engine RPM, transmission gear ratio, final drive ratio, and tire diameter.

Updated April 12, 2026
Free online tool
Planning and research use

Why this page exists

Drivetrain math is easier to read when RPM and gearing turn into a speed estimate instead of staying as separate spec numbers. This calculator helps visitors estimate vehicle speed from engine RPM, transmission gear ratio, final drive ratio, and tire diameter.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Gear speed calculator

Estimate vehicle speed from engine RPM, transmission gear ratio, final drive ratio, and tire diameter.

Result

64.6 mph

Estimated vehicle speed based on engine RPM, total drive ratio, and tire diameter.

Estimated vehicle speed64.6 mph

Estimated vehicle speed (km/h)104.0 km/h

Total drive ratio used3.730

Formula summaryRPM x tire diameter / (gear ratio x final drive x 336)

3,000 RPM with a 1.00 gear ratio, 3.73 final drive, and 27.0-inch tire diameter gives a speed estimate near 64.6 mph.
The total drive ratio used here is about 3.730, which is the transmission gear ratio multiplied by the final drive ratio.
Use this as a planning estimate only, because real speed can differ with tire growth, slip, and drivetrain factors that simple gearing math does not capture.

This is a drivetrain planning estimate only. Real-world speed can vary with tire growth, slip, converter behavior, drivetrain losses, and how closely the tire size matches its loaded rolling diameter.

Planning note

Last updated April 12, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Enter engine RPM, transmission gear ratio, final drive ratio, and tire diameter.

The calculator multiplies the transmission and final drive ratios to find the total drive ratio.

It then applies a standard gear-speed formula to estimate vehicle speed.

Understanding your result

This is a drivetrain planning estimate, not a road-speed guarantee. Tire growth, slip, converter behavior, and real rolling diameter can all change real-world speed.

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Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Translate gearing and RPM into a speed estimate

A quick speed estimate can make it easier to see what a gear setup may do before making changes.

Compare different final drive or tire setups

Changing one input at a time can show how gearing or tire diameter affects the speed result.

Use it with other drivetrain tools

Gear-speed estimates can make more sense when paired with gear ratio, tire size, or engine tools.

FAQ

Common questions

How is speed estimated here?

The calculator combines the transmission gear ratio and final drive ratio into a total drive ratio, then uses that ratio with RPM and tire diameter to estimate vehicle speed.

Why does tire diameter matter?

Tire diameter changes how far the vehicle travels per wheel rotation, so it directly affects the speed estimate.

Why can real speed differ from the estimate?

Loaded tire diameter, converter slip, tire growth, drivetrain losses, and measurement conditions can all shift real-world speed.

Related tools

Keep comparing

Use these related tools to compare nearby scenarios, check a second estimate, or keep narrowing down the right decision.

Auto ToolsUpdated April 12, 2026