What is a gear ratio?

A gear ratio is a mechanical ratio that defines the relationship between the rotational speeds of two or more gears. A 4:1 ratio means the driving (input) gear must turn 4 times to make the driven (output) gear turn once, resulting in higher torque but lower speed.

What does a 'high' vs. 'low' gear ratio mean?

This can be confusing. A 'low gear' (like 1st gear) has a numerically high ratio (e.g., 4.10:1) and provides high torque for acceleration. A 'high gear' (like 6th gear) has a numerically low ratio (e.g., 0.67:1) and provides high speed at lower RPM for fuel efficiency.

How do I find my tire diameter?

You can measure it directly or calculate it from the tire's sidewall code (e.g., 265/70R17). We recommend using a dedicated 'Tire Size Calculator' for the most accurate diameter in inches.

What is the difference between axle ratio and transmission ratio?

The transmission ratio is the gear you are currently in (1st, 2nd, etc.). The axle ratio (or differential ratio) is a fixed ratio in the differential that provides a final stage of torque multiplication before the wheels. Your total 'Final Drive Ratio' is the transmission ratio multiplied by the axle ratio.

Why does gear ratio affect fuel economy?

Gearing determines how hard the engine must work (RPM) to maintain a certain speed. A numerically low 'highway gear' (overdrive) allows the engine to spin at a lower, more efficient RPM while cruising, thus saving fuel. A high numerical ratio (low gear) forces the engine to spin faster, using more fuel but providing more power.

Gear Ratio Calculator - Calculate Speed, RPM & Ratios

Calculate simple gear ratios from teeth counts, or find your vehicle's speed (MPH/KPH) based on engine RPM, tire diameter, axle, and transmission ratios.

Full original guide (expanded)

Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

\[\text{Gear Ratio} = \frac{T_{\text{driven}}}{T_{\text{driving}}}\]

\text{Gear Ratio} = \frac{T_{\text{driven}}}{T_{\text{driving}}}

Formula (extracted LaTeX)

\[\text{FDR} = R_{\text{transmission}} \times R_{\text{axle}}\]

\text{FDR} = R_{\text{transmission}} \times R_{\text{axle}}

Formula (extracted LaTeX)

\[\text{Speed (MPH)} = \frac{\text{RPM} \times D_{\text{tire}}}{\text{FDR} \times 336.13}\]

\text{Speed (MPH)} = \frac{\text{RPM} \times D_{\text{tire}}}{\text{FDR} \times 336.13}

Formula (extracted text)

$ \text{Gear Ratio} = \frac{T_{\text{driven}}}{T_{\text{driving}}} $

Formula (extracted text)

$ \text{FDR} = R_{\text{transmission}} \times R_{\text{axle}} $

Formula (extracted text)

$ \text{Speed (MPH)} = \frac{\text{RPM} \times D_{\text{tire}}}{\text{FDR} \times 336.13} $

Variables and units

No variables provided in audit spec.

Sources (authoritative):

Home — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/
Lifestyle Everyday — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/lifestyle-everyday
Automotive — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/subcategories/automotive
Tire Size Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/tire-size
Fuel Economy (MPG) Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/fuel-economy-calculator
Engine Displacement Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/engine-displacement-calculator
Horsepower Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/horsepower

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
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Formulas

(Formulas preserved from original page content, if present.)

Version 0.1.0-draft

Citations

Add authoritative sources relevant to this calculator (standards bodies, manuals, official docs).

Changelog

0.1.0-draft — 2026-01-19: Initial draft (review required).