Gear inches is the diameter, in inches, of the wheel a penny-farthing would need to roll the same distance per pedal turn as your geared bike — the math is wheel diameter × (chainring ÷ cog). It collapses chainring, cog and wheel size into a single comparable number, so a 50×16 on a 700c (about 82 gear inches) and a 34×11 on a 650b are directly comparable. Bigger gear inches means a harder, faster gear; smaller means an easier climbing gear. It is the oldest and still most widely understood way to compare bike gears across drivetrains.

Is a bigger or smaller gear ratio better?

Neither — it depends on what you want. A larger ratio (more driver teeth per driven tooth) gives you more output speed per input turn, which is a higher, faster gear that takes more force to turn; great for descents and flats. A smaller ratio is a lower, easier gear that spins up quickly and climbs well but tops out at a lower speed. On a bike you want a wide spread of ratios so you can keep a comfortable cadence whether you are sprinting or grinding up a 12% grade. In machinery, you pick the ratio that lands your motor in its efficient RPM band at the load you need.

How does cadence relate to speed?

For a fixed gear, road speed is directly proportional to cadence — pedal twice as fast and you go twice as fast, up to the point you spin out. The tool computes it as ratio × wheel circumference × cadence, converted to km/h and mph. That is why pros hold a steady 90–100 rpm and shift gears to change speed rather than mashing harder in one gear — spinning a moderate gear fast is more efficient and easier on your knees than grinding a big gear slowly.

Why do torque and RPM move in opposite directions?

Because power is conserved (minus friction losses), and power equals torque times rotational speed. A gear set can trade one for the other but cannot create power. A 3:1 reduction makes the output shaft turn at one-third the speed but with three times the torque; an overdrive trades torque away for speed. This is the whole point of a gearbox — match a motor that is happiest at a fixed RPM to a load that needs either high torque (climbing, starting) or high speed (cruising).

Pick a climbing gear for a steep route

You are about to ride a route with a sustained 12% grade and want to be sure your lowest gear is easy enough. Switch to bike mode, enter your smallest chainring and largest cog (say 34×34), pick your wheel size, and read the gear inches — anything under about 25 is a genuine bailout gear. Set cadence to 70 and you will see the crawl speed that gear gives you, so you know whether you can keep momentum or will be walking.

Compare two drivetrains apples to apples

You are deciding between a 2× road setup (50/34 front, 11–32 rear) and a 1× gravel setup (40 front, 10–44 rear). Punch the extreme combinations of each into bike mode and compare gear inches: the highest gear tells you top-end speed, the lowest tells you climbing range. Because gear inches folds chainring, cog and wheel size into one number, you can rank the two systems directly instead of squinting at tooth counts.

Size a gear reduction for a small machine

You have a motor that runs best at 3000 RPM but your output shaft needs to spin near 750 RPM with extra torque. Use the general mode: a 4:1 ratio (e.g. a 60-tooth gear driven by a 15-tooth pinion) drops 3000 RPM to 750 and multiplies torque 4×. Enter the input RPM and the tool confirms the output speed and torque multiplier so you can check the reduction lands your motor in its happy band before you order gears.

Check the speed gain from a chainring swap

You are thinking of swapping a 50-tooth chainring for a 53 to go faster on flat group rides. Enter both with your usual cog and cadence in bike mode and read the km/h for each — the difference at 95 rpm is usually a couple of km/h, which tells you whether the upgrade is worth it or whether you would just spin out and lose your climbing gears.

Set a turbo-trainer gear for a target speed

Your workout calls for holding 30 km/h on the trainer. Pick a wheel size, set the cadence you want to hold (say 90), then try chainring/cog combinations until the speed readout hits 30. Now you know exactly which gear to be in before the interval starts, instead of fumbling with shift levers mid-effort.

Gear Ratio Calculator — transmission ratio, bike gear inches, development & speed

Gear & transmission ratio plus bicycle gear inches, development and speed from cadence — exact, browser-only

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Driver (input) teeth

Driven (output) teeth

Input speed (RPM)

Gear ratio

2:1

reduction — output turns slower, torque multiplied

Output speed

500 RPM

Torque multiplier

2 × input torque

What this tool does

Two calculators in one, built for cyclists and anyone doing mechanical or automotive gearing math. The general mode takes a driver and a driven gear tooth count and returns the gear ratio, and given an input RPM it computes the output shaft RPM and the torque multiplier — a reduction (ratio above 1) slows the output and multiplies torque, an overdrive (ratio below 1) does the opposite. The bicycle mode takes your chainring and cog teeth, picks a wheel size from the presets (700c, 650b, 26-inch, 27.5 and 29 MTB), and reports the gear ratio, gear inches (the classic comparison metric), development in metres per pedal stroke, and — with a cadence in pedal RPM — your road speed in both km/h and mph. A 50×16 on a 700×25c at 90 rpm rolls about 35.5 km/h. Every input lives in the URL so a share link reproduces the exact gear, and nothing leaves your browser.

Tool details

Input: Text + Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 11 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Student; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Gear Ratio Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Pick a climbing gear for a steep route
You are about to ride a route with a sustained 12% grade and want to be sure your lowest gear is easy enough. Switch to bike mode, enter your smallest chainring and largest cog (say 34×34), pick your wheel size, and read the gear inches — anything under about 25 is a genuine bailout gear. Set cadence to 70 and you will see the crawl speed that gear gives you, so you know whether you can keep momentum or will be walking.
Compare two drivetrains apples to apples
You are deciding between a 2× road setup (50/34 front, 11–32 rear) and a 1× gravel setup (40 front, 10–44 rear). Punch the extreme combinations of each into bike mode and compare gear inches: the highest gear tells you top-end speed, the lowest tells you climbing range. Because gear inches folds chainring, cog and wheel size into one number, you can rank the two systems directly instead of squinting at tooth counts.
Size a gear reduction for a small machine
You have a motor that runs best at 3000 RPM but your output shaft needs to spin near 750 RPM with extra torque. Use the general mode: a 4:1 ratio (e.g. a 60-tooth gear driven by a 15-tooth pinion) drops 3000 RPM to 750 and multiplies torque 4×. Enter the input RPM and the tool confirms the output speed and torque multiplier so you can check the reduction lands your motor in its happy band before you order gears.
Check the speed gain from a chainring swap
You are thinking of swapping a 50-tooth chainring for a 53 to go faster on flat group rides. Enter both with your usual cog and cadence in bike mode and read the km/h for each — the difference at 95 rpm is usually a couple of km/h, which tells you whether the upgrade is worth it or whether you would just spin out and lose your climbing gears.
Set a turbo-trainer gear for a target speed
Your workout calls for holding 30 km/h on the trainer. Pick a wheel size, set the cadence you want to hold (say 90), then try chainring/cog combinations until the speed readout hits 30. Now you know exactly which gear to be in before the interval starts, instead of fumbling with shift levers mid-effort.

Common pitfalls

Swapping the driver and driven numbers. Ratio is driver ÷ driven; on a bike that is chainring ÷ cog. Flip them and a 50×16 (ratio 3.1) reads as 0.32, which is nonsense for a road gear. The driver is the gear you turn (front/input), the driven is the one being turned (rear/output).
Comparing gear inches across different wheel sizes by tooth count alone. A 40-tooth chainring on a 29-inch wheel is a much bigger gear than a 40 on a 26-inch wheel. Always compare gear inches or development, which include wheel size, not raw chainring and cog numbers.
Forgetting that speed scales with cadence. A gear that feels fine at 80 rpm is over-geared if your sustainable cadence on a climb is 60 — the speed and effort both change with cadence, so set a realistic cadence before reading the speed.

Privacy

Every calculation — ratio, output RPM, gear inches, development and speed — is plain JavaScript that runs in your browser tab. No tooth count, wheel size or cadence ever leaves the page, and there is no external API call or logging. The one thing to know: the shareable URL encodes your current inputs in the query string (for example ?m=bike&cr=50&cg=16), so if you paste a share link somewhere, the destination server's access log will see those numbers. Bike and machine gearing are not sensitive, so this is harmless — but if you would rather not, just copy the result text instead of sharing the URL.

FAQ

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Gear Ratio Calculator — transmission ratio, bike gear inches, development & speed

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Gear Ratio Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Pick a climbing gear for a steep route

Compare two drivetrains apples to apples

Size a gear reduction for a small machine

Check the speed gain from a chainring swap

Set a turbo-trainer gear for a target speed

Common pitfalls

Privacy

FAQ

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