Bicycle Gear Calculator
Enter chainring and rear-cog tooth counts, measured wheel circumference and crank cadence. Compare every combination, inspect exact ratio matches on an aligned chart, and download the full gear table.
Drivetrain and measured wheel
Enter up to 8 unique chainrings and 50 unique rear cogs, using commas, semicolons or spaces. Use your wheel’s rolling circumference, not its diameter. Changing circumference units reinterprets the unchanged input number; output-unit changes convert results. Defaults are editable examples, not an equipment recommendation.
Aligned gear overlap chart
Tap a dot or tab to it and press Enter to inspect a gear. Horizontally aligned dots are equal ratios; nearby dots may overlap visually at this scale. The table and exact-ratio matches below distinguish them. Scroll the chart on small screens.
Selected gear: 50 / 11
Ratio = 50 ÷ 11
Rollout in metres = 2.105 × 50/11
Speed in km/h = rollout in metres × 90 × 60 ÷ 1000
Gear inches = (circumference in metres ÷ π ÷ 0.0254) × ratio = 119.9074
Gear inches use the diameter implied by your rolling circumference, not a nominal rim or tire size. Exact ratio equivalents: none in this worksheet. Equal ratios also have equal rollout and speed under the same circumference/cadence inputs.
All gear combinations
| Ring / cog | Ratio | Rollout (m) | Speed (km/h) | Gear inches | Equal ratios |
|---|---|---|---|---|---|
| 1.0625 | 2.2366 | 12.0774 | 28.0283 | None | |
| 1.2143 | 2.5561 | 13.8028 | 32.0324 | None | |
| 1.36 | 2.8628 | 15.4591 | 35.8763 | None | |
| 1.5455 | 3.2532 | 17.5672 | 40.7685 | None | |
| 1.5625 | 3.2891 | 17.7609 | 41.2182 | None | |
| 1.7 | 3.5785 | 19.3239 | 44.8454 | None | |
| 1.7857 | 3.7589 | 20.2982 | 47.1065 | None | |
| 1.8889 | 3.9761 | 21.471 | 49.8282 | None | |
| 2 | 4.21 | 22.734 | 52.7592 | None | |
| 2.125 | 4.4731 | 24.1549 | 56.0567 | None | |
| 2.2727 | 4.7841 | 25.8341 | 59.9537 | None | |
| 2.4286 | 5.1121 | 27.6056 | 64.0648 | None | |
| 2.5 | 5.2625 | 28.4175 | 65.949 | None | |
| 2.6154 | 5.5054 | 29.7291 | 68.9928 | None | |
| 2.7778 | 5.8472 | 31.575 | 73.2767 | None | |
| 2.8333 | 5.9642 | 32.2065 | 74.7423 | None | |
| 3.0909 | 6.5064 | 35.1344 | 81.537 | None | |
| 3.125 | 6.5781 | 35.5219 | 82.4363 | None | |
| 3.5714 | 7.5179 | 40.5964 | 94.2129 | None | |
| 3.8462 | 8.0962 | 43.7192 | 101.4601 | None | |
| 4.1667 | 8.7708 | 47.3625 | 109.9151 | None | |
| 4.5455 | 9.5682 | 51.6682 | 119.9074 | None |
The table includes all 22 combinations. Equal-ratio detection reduces integer tooth counts exactly; it does not compare rounded display values. Table order does not change exported row order.
CSV includes every combination in entered ring/cog order, input circumference/cadence, chosen output units, exact reduced ratios and numeric values to 15 significant digits. Import ratio columns as text to avoid spreadsheet date conversion. Display values use up to four decimals, with scientific notation for very small nonzero values.
What this model assumes
One crank revolution turns the wheel by the front-to-rear tooth ratio. This assumes direct chain drive, with no additional internal-hub or gearbox ratio and no rolling slip. Cadence is crank revolutions per minute, not wheel revolutions.
The speed is a geometric result at the supplied cadence. It does not estimate power, achievable road speed, tire deformation, efficiency, terrain, chainline, derailleur capacity or component compatibility. Tooth counts accept 1–2,000; circumference accepts a positive decimal up to 1,000,000 selected units; cadence accepts 0–1,000 rpm. These arithmetic bounds are not equipment recommendations.
Geometric estimates from supplied tooth counts, wheel circumference and cadence. No equipment compatibility, safety, terrain, power or training recommendation. Calculations stay in your browser. Inputs are not automatically saved; export before leaving.
Common questions
- How is bicycle gear ratio calculated?
- Divide chainring teeth by rear-cog teeth. A 50-tooth chainring and 25-tooth cog give ratio 2, meaning two wheel revolutions per crank revolution under the direct-chain-drive model.
- How are rollout and speed calculated?
- Rollout is wheel circumference multiplied by gear ratio. With a 2 m circumference and ratio 2, rollout is 4 m per crank revolution. At 60 crank rpm, speed is 4 × 60 × 60 / 1000 = 14.4 km/h. Output can be converted to feet per revolution and miles per hour.
- Should I enter wheel diameter or circumference?
- Enter rolling circumference, the distance covered by one wheel revolution, in mm, cm, m or inches. Diameter is a different measurement. Changing the circumference-unit selector reinterprets the unchanged number; changing an output unit converts the result.
- What does the overlap chart show?
- Each row represents a chainring, and each dot is a rear-cog combination on one shared ratio axis. Equal horizontal positions represent equal ratios. Select dots with a pointer or keyboard to inspect their values. Nearby points may overlap visually; the full table and exact-equivalent list distinguish them.
- How are equal gears identified?
- The calculator reduces tooth-count fractions with integer arithmetic. For example, 50/25 and 40/20 are both exactly 2/1. It does not use rounded display values to infer equality. Under the same wheel circumference and cadence, equal ratios have equal rollout and geometric speed.
- What are gear inches and range?
- Gear inches are the wheel diameter implied by the supplied circumference, in inches, multiplied by gear ratio. Highest/lowest compares the largest and smallest ratios. The percentage shown is the increase from the lowest ratio, (highest/lowest − 1) × 100, rather than highest/lowest expressed as a percent.
- Does this predict real speed or component compatibility?
- No. It assumes direct chain drive and rolling without slip. It does not model internal hub ratios, power, terrain, losses, tire deformation, chainline, derailleur capacity or achievable speed. The calculations are descriptive geometry, not compatibility, safety or training recommendations.
- What are the input and export limits?
- Enter up to eight unique chainrings and 50 unique rear cogs, with 1–2,000 teeth each. Circumference supports six decimal places and up to 1,000,000 selected units; cadence supports 0–1,000 rpm with three decimals. CSV includes every combination with 15-significant-digit numeric values. Import exact ratios as text to prevent spreadsheet date conversion. Inputs stay local and are not saved automatically.
Geometric estimates from supplied tooth counts, wheel circumference and cadence. No equipment compatibility, safety, terrain, power or training recommendation.