Bike Gear Calculator

How to use the Bike Gear Calculator

What this calculator does

This calculator compares a continuous range of front chainring tooth counts with a continuous range of rear cog tooth counts. For every pairing, it calculates the gear ratio and, when a wheel diameter is supplied, gear inches. It is useful for understanding whether a proposed drivetrain offers suitably low climbing gears, suitably high cruising gears, or overlapping combinations. It does not predict speed by itself, because road speed also depends on cadence, tire rollout, load, gradient, wind, and drivetrain efficiency. It also does not model the internal ratios of planetary hub gears.

When to use it

Use it when comparing two cassettes, planning a chainring change, checking the range of a touring or gravel setup, or translating tooth counts into a common measure that is easier to compare across wheel sizes. The Cycling UK guide to measuring bicycle gears explains why ratio, range, and overlap are more informative than simply counting nominal gears.

How to calculate

1. The calculator opens with a ready-to-use demonstration: chainrings from 42 to 48 teeth, cogs from 10 to 24 teeth, and a 28-inch wheel. The results and example XLSX workbook are available immediately.
2. Replace Chainring minimum and Chainring maximum with the smallest and largest front tooth counts you want to compare. Enter whole numbers only.
3. Replace Cog minimum and Cog maximum with the smallest and largest rear tooth counts. The calculator includes every integer between each minimum and maximum, so a 10-to-24 range creates fifteen cog columns.
4. Enter Wheel diameter as the effective outside diameter in inches. A decimal such as 27.5 is valid. Use a period as the decimal separator; commas and scientific notation are rejected to avoid ambiguous interpretation.
5. Read the live summary and both matrices. Select Download Excel to export the current typed inputs and all calculated combinations to a validated workbook. Select Reset to clear the demonstration and all calculated content. After Reset, the Excel action stays disabled until every required field contains a complete valid set again.

Input guide

Chainring minimum is a required whole-number tooth count from 1 to 120; 42 is a realistic example. Lowering it usually lowers the easiest ratio and gear inches. A common mistake is entering a diameter or model name instead of the actual tooth count. Chainring maximum is also required, uses the same range, and cannot be below the minimum; 48 is the startup value. Raising it increases the hardest available gearing. Cog minimum is the smallest rear sprocket, required from 1 to 120 teeth; 10 is the example. Lower values create higher, harder ratios. Cog maximum is the largest rear sprocket, required in the same range and not below the minimum; 24 is the example. Larger values create lower, easier ratios. Wheel diameter is a required positive decimal from 1 to 100 inches; 28 is the example. It changes gear inches proportionally but does not change the dimensionless gear ratio. Measure the effective outside tire diameter when precision matters rather than relying only on a nominal rim label.

Output guide

Gear ratio range shows the lowest and highest front-teeth ÷ rear-teeth results. Easiest combination identifies the minimum ratio and its rounded gear inches; lower values generally favor climbing and low-speed control. Hardest combination identifies the maximum ratio and its gear inches; higher values generally favor more distance per crank revolution. Overall gear range is the highest ratio divided by the lowest ratio, expressed as a percentage; 100% would mean no range at all, while larger values indicate a broader spread. Combination count is the exact number of integer tooth-count pairings generated. The Gear ratio matrix reports exact comparative ratios to two decimals. The Gear inches matrix multiplies each ratio by wheel diameter and displays the nearest whole inch. These outputs are mathematical comparisons, not recommendations for derailleur capacity, chain length, frame clearance, or component compatibility.

Worked example

With the startup values, the easiest pairing is the 42-tooth chainring with the 24-tooth cog: 42 ÷ 24 = 1.75. Multiplying by the 28-inch wheel gives 49 gear inches. The hardest pairing is 48 with 10: 48 ÷ 10 = 4.80, and 28 × 4.80 = 134.4, displayed as 134 gear inches. The complete range is 4.80 ÷ 1.75 × 100 = 274.29%, and the seven chainring values multiplied by fifteen cog values produce 105 combinations. For a practical explanation of how front chainrings, rear cogs, and effort interact, see REI's guide to using bicycle gears.