bicycle gear calculator

Why bicycle gearing matters

Bicycle gearing controls how far your bike travels with each pedal revolution. A small change in chainring or cassette tooth count can dramatically alter climbing comfort, cruising speed, and pedaling efficiency. If your gearing is too hard, climbs become a grind. If it is too easy, you may “spin out” on flats and descents.

This calculator gives you practical numbers that are useful for choosing chainrings, comparing cassettes, planning a bike build, or checking whether your current setup matches your riding style.

What the calculator shows

1) Gear ratio

Gear Ratio = front teeth ÷ rear teeth. A ratio of 3.00 means one full crank turn makes the rear wheel turn about three times (ignoring drivetrain losses).

2) Gear inches

Gear Inches = gear ratio × wheel diameter (inches). This classic cycling metric is great for comparing setups quickly. Higher gear inches generally mean harder pedaling but higher speed at the same cadence.

3) Development (rollout)

Development = wheel circumference × gear ratio. This tells you how many meters the bike moves per crank revolution. It is often the clearest real-world measure of “how big” a gear feels.

4) Speed from cadence

Once rollout is known, speed is simple:

• km/h = development × cadence × 60 ÷ 1000
• mph = km/h × 0.621371

5) Gain ratio (optional)

Gain ratio includes crank length, providing a more body-centered view of leverage. It is useful if you compare bikes with different crank lengths or fit preferences.

How to use these numbers in the real world

For climbing

Focus on lower gears (smaller gear inches and lower development). They let you keep cadence steady on steep grades and reduce knee stress. If you ride mountains often, prioritize a cassette with a larger biggest cog.

For road speed and group rides

Look at your high gears at 85–100 RPM. If your top-end speed feels limited on flats, you may benefit from a larger chainring, a smaller top cog, or both.

For mixed terrain and commuting

Choose a balanced spread. You want a low enough climbing gear and a high enough cruising gear without huge jumps between cassette cogs.

Example comparisons

Setup	Wheel	Ratio	Gear Inches	Speed @ 90 RPM
50 / 17	27.5"	2.94	80.9	~31.1 km/h (19.3 mph)
34 / 34	27.5"	1.00	27.5	~10.6 km/h (6.6 mph)
52 / 11	27"	4.73	127.6	~54.8 km/h (34.1 mph)

Choosing better gears: practical checklist

• Track your usual cadence range (many riders are comfortable around 80–95 RPM).
• Check your hardest local climb and your desired climbing cadence.
• Estimate your desired cruising speed on flats.
• Use the calculator to test multiple chainring/cassette combinations.
• Prefer smoother cassette jumps if cadence consistency matters to you.

Common mistakes riders make

• Only looking at top speed: low-end climbing gears matter more for most riders.
• Ignoring cadence: speed numbers are meaningless without realistic RPM.
• Using nominal wheel size only: tire width changes true diameter and rollout.
• Choosing pro-level gearing: aggressive gearing can hurt comfort and consistency.

Final thought

The best gearing is the one that matches your terrain, fitness, and goals. Use this calculator as a quick decision tool: test ideas, compare setups, and aim for the cadence range where you produce smooth, repeatable power. Good gear choices make every ride feel more controlled, efficient, and enjoyable.