What are gear inches?

Gear inches express the effective diameter of a directly driven wheel that would produce the same mechanical advantage as the actual drivetrain. A higher gear-inch value means a harder gear (more distance per pedal stroke), while a lower value indicates an easier gear. The measurement allows comparison across different wheel sizes and component combinations.

How does wheel diameter affect the calculation?

Wheel diameter scales the final gear-inch result proportionally. Larger wheels increase the gear-inch value for any given chainring-cog combination because each wheel rotation covers more ground. The calculator requires the nominal wheel diameter in inches; common road sizes include 27 inches (traditional) and 28 inches (700c), while mountain bikes typically use 26, 27.5, or 29 inches.

Why does a smaller rear cog produce a higher gear?

A smaller rear cog has fewer teeth, so the chain wraps around it fewer times per revolution. This increases the ratio of chainring teeth to cog teeth, causing the rear wheel to spin faster relative to pedal cadence. The result is a higher gear-inch value, meaning more resistance and greater distance traveled per pedal stroke.

Can this calculator compare gearing across different bikes?

Yes. Gear inches normalize comparisons by accounting for both drivetrain ratios and wheel size. A road bike with 50/16 gearing on 700c wheels can be directly compared to a mountain bike with 32/11 gearing on 29-inch wheels by calculating the gear inches for each setup. The tool does not account for tire width or actual rolling radius variations.

What is the difference between gear inches and gear ratio?

Gear ratio is the simple division of chainring teeth by rear cog teeth (e.g., 50 ÷ 16 = 3.125). Gear inches multiply this ratio by wheel diameter to produce a value that accounts for how far the bike travels per pedal revolution. Gear inches provide a more complete picture of mechanical advantage because they incorporate wheel size, while ratio alone does not.

Cycling

Bike Gear Ratio Calculator

Calculate gear inches from chainring, rear cog, and wheel diameter to compare drivetrain ratios.

Last updated: 22 April 2026

What this tool does

This calculator computes gear inches, a dimensionless measure of bicycle gearing, using the standard cycling mechanics formula: (chainring teeth ÷ rear cog teeth) × wheel diameter. It requires three inputs—chainring tooth count, rear cog tooth count, and wheel diameter in inches—and outputs the gear inches value, which represents the effective diameter of a directly driven wheel that would produce the same mechanical advantage. The gear ratio metric originated in the penny-farthing era and remains the standard method for comparing drivetrain configurations across different bicycles and wheelsets.

Inputs

Result

—

Formula Used

Gear inches = \frac{F}{R} \times D

F

Front chainring teeth

R

Rear cog teeth

D

Wheel diameter in inches

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How Bike Gear Ratio Calculator works

This calculator computes gear inches, a measurement that expresses how far a bicycle travels forward with one complete pedal revolution. It multiplies the ratio of front chainring teeth to rear cog teeth by the wheel diameter. A higher gear-inch value indicates a harder gear (more resistance, greater distance per pedal stroke), while a lower value indicates an easier gear. The tool accepts chainring and cog tooth counts plus wheel diameter in inches, then returns the gear-inch measurement and the numeric ratio.

The formula

The calculation follows the classic gear-inch formula:

Gear inches = (Chainring teeth ÷ Rear cog teeth) × Wheel diameter (inches)

For example, a 50-tooth chainring paired with a 16-tooth cog on a 27-inch wheel yields (50 ÷ 16) × 27 = 84.4 gear inches. The intermediate ratio of 3.125 means the rear wheel rotates 3.125 times for every pedal revolution. Multiplying by wheel diameter converts this ratio into the effective diameter of the imaginary directly driven wheel that would produce the same mechanical advantage.

Where this method is most accurate

Gear inches provide a consistent comparison standard across different wheel sizes and drivetrain setups. The calculation assumes a perfectly circular wheel with the stated diameter; actual rolling radius varies slightly with tire width, pressure, and rim design. The method does not account for chainline efficiency, drivetrain friction, or pedaling cadence effects on power delivery. Gear inches serve best as a relative comparison tool rather than an absolute predictor of cycling speed or effort, since rider power output, aerodynamics, terrain, and wind conditions all influence actual performance.

What this tool does not do

This calculator computes a mechanical ratio and does not recommend specific gearing choices for training, racing, or terrain. It does not estimate cycling speed, power output, caloric expenditure, or optimal cadence ranges. The tool does not diagnose mechanical issues, predict component wear rates, or advise on drivetrain compatibility. It performs a single arithmetic operation using the values entered and returns the resulting gear-inch measurement.

Disclaimer

This tool is provided for educational and informational purposes only. It is not a substitute for professional coaching, bicycle fitting services, or mechanical advice from qualified technicians. Every cyclist's physiology, experience level, and riding conditions differ. Numbers generated by this calculator represent mathematical estimates based on the formula shown; they do not constitute training guidance or performance guarantees.

Questions

What are gear inches?: Gear inches express the effective diameter of a directly driven wheel that would produce the same mechanical advantage as the actual drivetrain. A higher gear-inch value means a harder gear (more distance per pedal stroke), while a lower value indicates an easier gear. The measurement allows comparison across different wheel sizes and component combinations.
How does wheel diameter affect the calculation?: Wheel diameter scales the final gear-inch result proportionally. Larger wheels increase the gear-inch value for any given chainring-cog combination because each wheel rotation covers more ground. The calculator requires the nominal wheel diameter in inches; common road sizes include 27 inches (traditional) and 28 inches (700c), while mountain bikes typically use 26, 27.5, or 29 inches.
Why does a smaller rear cog produce a higher gear?: A smaller rear cog has fewer teeth, so the chain wraps around it fewer times per revolution. This increases the ratio of chainring teeth to cog teeth, causing the rear wheel to spin faster relative to pedal cadence. The result is a higher gear-inch value, meaning more resistance and greater distance traveled per pedal stroke.
Can this calculator compare gearing across different bikes?: Yes. Gear inches normalize comparisons by accounting for both drivetrain ratios and wheel size. A road bike with 50/16 gearing on 700c wheels can be directly compared to a mountain bike with 32/11 gearing on 29-inch wheels by calculating the gear inches for each setup. The tool does not account for tire width or actual rolling radius variations.
What is the difference between gear inches and gear ratio?: Gear ratio is the simple division of chainring teeth by rear cog teeth (e.g., 50 ÷ 16 = 3.125). Gear inches multiply this ratio by wheel diameter to produce a value that accounts for how far the bike travels per pedal revolution. Gear inches provide a more complete picture of mechanical advantage because they incorporate wheel size, while ratio alone does not.

Sources & Methodology

Gear inches = (chainring teeth / rear cog teeth) × wheel diameter (inches). This formula, standardized in cycling mechanics literature, converts drivetrain gearing into an equivalent directly driven wheel diameter. The method originated in the penny-farthing era when wheel size directly determined gear ratio.

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