The Bicycle Gear Calculator and the Bicycle Power Calculator both analyze a cycling setup, but they answer different questions. The gear calculator works from the drivetrain — chainring and rear-cog tooth counts, cadence, and a measured wheel rollout — and reports gear ratio, gear inches, development, and the theoretical no-slip speed at your cadence. The power calculator works from motion and resistance — ground speed, grade, mass, rolling resistance, aerodynamic drag, wind, and drivetrain efficiency — and estimates the steady-state mechanical power the scenario requires. If your question is about gears, pick the gear tool; if it is about watts for a given speed and resistance, pick the power tool.
Both pages are explicit that their results are arithmetic, not prescriptions: the gear calculator does not prescribe gearing, cadence, training, safety, or performance, and the power calculator reports sensitivity arithmetic rather than performance, fitness, or equipment guidance.
What each calculator does
The Bicycle Gear Calculator computes the external drivetrain relationship: gear ratio is chainring teeth divided by rear-cog teeth, development is measured wheel circumference multiplied by that ratio, gear inches is the effective diameter in inches times the ratio, and theoretical speed is development times cadence, converted from meters per minute to km/h and mph. It is built around a measured loaded wheel rollout — inflate the tire, mark the tire and ground at the valve, roll one revolution, and measure between the marks. Its limits are stated plainly: the result is theoretical no-slip rollout, so tire slip, dynamic deformation, drivetrain loss, wind, grade, acceleration, and rider power are not modeled.
The Bicycle Power Calculator estimates steady-state mechanical power from force components: rolling force is Crr times mass times 9.80665, grade force is mass times 9.80665 times grade as a fraction, and aerodynamic force is half times air density times CdA times relative air speed squared. Wheel power is total force times ground speed, and input power divides that by drivetrain efficiency. All of the empirical factors — coefficients, density, wind, efficiency — are scenario values you supply, and its article emphasizes that results are sensitivity arithmetic with the uncertainty you enter.
Side-by-side comparison
| Feature | Bicycle Gear calculator | Bicycle Power calculator |
|---|---|---|
| Central question | What gearing do I have, and what speed at my cadence? | How much power does this speed, grade, and resistance need? |
| Key inputs | Tooth counts, cadence, measured wheel rollout | Speed, grade, mass, Crr, CdA, density, wind, efficiency |
| Main outputs | Gear ratio, gear inches, development, theoretical speed | Force components and wheel/input power |
| Wheel measurement | Required — measured loaded rollout | Not used directly |
| Resistances modeled | None — theoretical no-slip rollout | Rolling, grade, aerodynamic drag, drivetrain loss |
| Result type | Drivetrain and rollout geometry | Mechanical-power scenario with sensitivity |
When to use which
Use the Bicycle Gear Calculator when you are working with the drivetrain itself: comparing chainring and cog combinations, expressing a setup in gear inches or development, or estimating the theoretical speed at a given cadence. Its article’s workflow is the giveaway — the measured wheel rollout is the centerpiece, and the result is explicitly no-slip, cadence-driven speed.
Use the Bicycle Power Calculator when the question is about the effort required to hold a speed: how much power a climb or headwind demands at your mass and drag, or how a change in CdA or rolling resistance moves the requirement. Because every resistance factor is an entered scenario value, it is a tool for comparing scenarios, not a measurement of your fitness.
The two tools are adjacent in the same cycling topic: the gear calculator provides the gearing and cadence context around a measured cycling scenario, while the power calculator turns motion and resistance into watts. Pick by question — gearing and rollout, or power and resistance — rather than by bike.
Where to start
- Bicycle Gear Calculator — gear ratio, gear inches, development, and cadence-based speed.
- Bicycle Power Calculator — mechanical power from speed, grade, drag, and rolling resistance.