Free Tool

GEAR RATIO CALCULATOR

Every chainring and cog combination mapped to gear ratio, gear inches, development, and speed at cadence. See where your gearing overlaps and where the gaps are.

Quick presets

CHAINRING TEETH

Selected: 50/34T

CASSETTE

WHEEL / TYRE SIZE

Presets are nominal. A loaded rollout measurement gives the most accurate speed and development.

METHODOLOGY

Gear ratio: Chainring teeth divided by cog teeth. A 50/25 combination gives a ratio of 2.0 — each pedal revolution turns the rear wheel twice.

Gear inches: Gear ratio multiplied by the wheel diameter in inches. An old standard (dating back to penny-farthing comparisons) that remains the most intuitive way to compare gears across different wheel sizes.

Metres of development: Gear ratio multiplied by the wheel circumference (rollout) in metres. This is the distance the bike travels per pedal revolution. Widely used in continental Europe and in track cycling.

Rollout variation: Preset tyre circumferences are nominal. Rim width, fitted tyre width, pressure, load, tread, and casing change the real circumference. For precision, measure one loaded wheel revolution on level ground and use the custom rollout field.

Sources:The arithmetic is shown above. Nominal circumferences and cassette tooth sequences are checked against the named Garmin, Wahoo, Shimano, and SRAM sources below; gain ratio follows Sheldon Brown's original definition.

Last reviewed: 31 August 2026 · Tool version 1.1

Quick answer

Choose your chainrings, exact cassette sprockets and wheel rollout. The calculator divides front teeth by rear teeth, then uses wheel circumference to show gear inches, metres travelled per pedal revolution and speed at each cadence. It compares gearing geometry; it does not certify derailleur, chain, freehub or frame compatibility.

WHAT IT DOES

This is the canonical Roadman owner for bike gear ratio calculator intent. It maps every selected chainring-and-cog pair, identifies the easiest and hardest combinations, and makes duplicated or widely spaced gears visible before you buy a cassette. The companion gear-ratio guide owns explanatory intent and worked training examples.

Preset tooth sequences are tied to named Shimano and SRAM configurations. You can enter any cassette manually, and a custom loaded-rollout input prevents a nominal tyre label from pretending to be an exact circumference.

WHO IT'S FOR

→Road, gravel and sportive riders comparing cassette or chainring options
→Cyclists checking climbing gears before a hilly event or training camp
→Riders who want speed-at-cadence, development and gear inches from one input
→Mechanics and coaches who need a transparent table instead of a black-box recommendation

HOW IT WORKS

For each combination, raw gear ratio is chainring teeth divided by rear-cog teeth. Development is that ratio multiplied by wheel circumference in metres. Speed is development multiplied by cadence and 60, then divided by 1,000 for kilometres per hour. Gear inches use the same ratio multiplied by wheel diameter in inches. The calculator does not model tyre slip or drivetrain losses.

01
Enter the drivetrain you actually have
Choose a named preset only when its tooth sequence matches your cassette. Otherwise enter every rear cog manually and choose the matching chainring set.
02
Set wheel circumference
Use a nominal tyre preset for a quick comparison or measure one loaded wheel revolution and enter the millimetres as a custom rollout for the most accurate speed and development.
03
Calculate every combination
Read the easiest and hardest gears, then open individual cells to compare development and speed across practical cadences.
04
Check compatibility separately
Confirm maximum sprocket, total capacity, freehub body, chain length and approved chainring combinations in the exact component manuals before buying parts.

EXAMPLE CALCULATIONS

Compact road bike: 50/34, 11-28, 700x25c

· Wheel rollout: 2,105 mm
· Easiest: 34/28
· Hardest: 50/11

34/28 is a 1.21 ratio and 2.56 m development, or 13.8 km/h at 90 rpm. 50/11 is a 4.55 ratio and 9.57 m development, or 51.7 km/h at 90 rpm.

1x gravel bike: 40T, SRAM XPLR 10-44, 700x32c

· Wheel rollout: 2,155 mm
· Easiest: 40/44
· Hardest: 40/10

40/44 is a 0.91 ratio and 1.96 m development, or 9.4 km/h at 80 rpm. 40/10 is a 4.00 ratio and 8.62 m development, or 46.5 km/h at 90 rpm.

LIMITATIONS

Wheel presets are nominal: rim width, fitted tyre width, pressure, load and tread change the real rollout. The output assumes no tyre slip and reports kinematics, not the power needed for a gradient. A matching numerical ratio does not prove a cassette will work with a derailleur, freehub, chain, shifter or frame. Manufacturer compatibility and installation documents override this calculator.

When to get setup help

Ask a qualified mechanic to check component compatibility before a cassette, chainring or drivetrain change. Use a coach when the decision depends on your sustainable power, cadence under fatigue, event gradients or pacing rather than ratios alone. Persistent knee pain needs an appropriate clinical or bike-fit assessment, not a lower-gear guess from a calculator.

SOURCES & TRUST

Author

Anthony Walsh — Cycling Coach & Podcast Host

Evidence sources

Garmin wheel size and circumference table — nominal 700c rollout values and manual-measurement boundary
Wahoo tyre-size and wheel-circumference chart — loaded-rollout measurement guidance and sources of circumference variation
Shimano CS-R8000 cassette specification — 11-speed 11-25, 11-28, 11-30 and 11-32 sprocket sequences
Shimano CS-R7100 cassette specification — 12-speed 11-34 sprocket sequence
Shimano CS-HG710 dealer manual — 12-speed 11-36 sprocket sequence
SRAM Rival XG-1250 cassette — 12-speed 10-36 sprocket sequence and XDR boundary
SRAM PG-1130 cassette — 11-speed 11-42 sprocket sequence and drivetrain boundary
SRAM XPLR XG-1251 cassette — 12-speed 10-44 sprocket sequence
Sheldon Brown gain-ratio method — original gain-ratio definition and wheel/crank geometry

Reviewed by Anthony Walsh — calculator method, preset tooth sequence and source-to-claim review · Last reviewed 31 August 2026

Editorial standards · Report a correction

FREQUENTLY ASKED QUESTIONS

How do you calculate a bike gear ratio?+

Divide the number of teeth on the front chainring by the number on the selected rear cog. A 50-tooth chainring with a 25-tooth cog is 50 / 25 = 2.00. The rear wheel turns twice for each crank revolution, before accounting for wheel circumference.

What is a good gear ratio for climbing?+

There is no universal climbing ratio. Lower numbers are easier, but the right lowest gear depends on gradient, total system mass, sustainable power and the cadence you can hold when tired. Compare the calculator output with your real climbing files and event route rather than treating 1:1 as a rule.

What is the difference between gear ratio, gear inches and development?+

Gear ratio compares chainring teeth with rear-cog teeth. Gear inches applies that ratio to wheel diameter. Development applies it to wheel circumference and reports metres travelled per crank revolution. Development connects most directly to speed at a chosen cadence.

How accurate are the wheel-size presets?+

They are nominal starting values. Actual circumference changes with rim width, tyre casing, fitted width, pressure and rider load. For the most accurate result, mark the tyre, complete one loaded wheel revolution on level ground, measure the distance in millimetres and use custom rollout.

Does a lower gear ratio mean easier pedalling?+

At the same wheel speed, a lower ratio requires a higher cadence and less crank torque for the same rear-wheel torque, so it generally feels easier to turn. It does not reduce the external power required to move the rider up a hill at the same speed.

Will the calculator tell me whether a cassette fits my bike?+

No. It compares tooth counts only. Cassette and chainring compatibility also depends on freehub standard, number of speeds, shifter indexing, derailleur maximum sprocket and total capacity, chain length, chainline and frame clearance. Check the exact component manuals or ask a qualified mechanic.