Bike Gear Calculator Gear Ratios, Gear Inches, Development & Speed at Cadence, with Setup Comparison and Climb Check
See every gear on your bike at once: ratio, gear inches, metres of development, gain ratio and speed at your cadence. Compare two drivetrains side by side, spot duplicate and cross-chained gears, and check whether your lowest gear will get you up the climbs you ride.
Formulas per Sheldon Brown’s gear theory · wheel sizes per ISO 5775 (ETRTO) · cassette tooth counts from Shimano and SRAM specifications · Last reviewed October 23, 2026
Your drivetrain
Bike type UnitsMeasured rollout (optional)
Measure one full wheel turn with you seated on the bike. Leave blank to use the ISO size estimate.
Climb check
Selected gear · 50 × 11
52.3km/h at 90 rpm
Tap any cell in the gear chart to inspect that gear.
Chainring and cog drawn to scale
Gear chart Setup A
Gear ladder: Setup A vs B
Each dot is a gear, placed by speed at your cadence. Gaps show where shifts feel big; clusters show duplicated gears.
Climb check
—
A vs B
Shifting steps Setup A cassette
Insights
How do you calculate a bike gear ratio?
Gear ratio = chainring teeth ÷ cog teeth. A 50-tooth chainring with an 11-tooth cog is 50 ÷ 11 = 4.55, so the rear wheel turns 4.55 times for every pedal revolution.
Multiply the ratio by the wheel’s diameter to get gear inches (121.3 for 50×11 on a 700×28 wheel), or by its circumference to get development (9.68 m per pedal turn). Speed = development × cadence: at 90 rpm that is 52.3 km/h (32.5 mph).
How to use the bike gear calculator
- Pick your bike type. Road, gravel, MTB or fixie loads a typical drivetrain and wheel. It also sets the rolling resistance and riding position used by the climb check.
- Enter your chainrings and cassette. Type tooth counts in any format (“50, 34” or “11-12-13…”) or choose a Shimano or SRAM cassette preset. One chainring means a 1× setup.
- Set the wheel, tire, cadence and crank. These drive gear inches, development, gain ratio and speed. For the best accuracy, enter a measured rollout.
- Compare a second setup. Turn on Setup B to see what a new cassette or chainring would change: easier climbing, a higher top speed or smaller jumps between gears.
- Check your climbs. Enter a gradient, your weight with the bike, and the power you can hold. The calculator tells you the cadence you’d turn in your lowest gear, and the lowest gear you’d need to spin at 80 rpm.
Bike gear formulas: ratio, gear inches, development, gain ratio and speed
Gear ratio = chainring ÷ cog
Wheel diameter = ISO bead seat diameter + 2 × tire width (mm)
Gear inches = ratio × wheel diameter (in)
Development (m) = ratio × wheel circumference (m)
Gain ratio = ratio × wheel radius ÷ crank length
Speed (km/h) = development × cadence × 60 ÷ 1000
Gear range (%) = highest ratio ÷ lowest ratio × 100
Gear inches is the traditional English measure, the diameter of the equivalent penny-farthing wheel. Development (or rollout) is the European measure: how far the bike travels per pedal stroke. Gain ratio, popularised by Sheldon Brown, also takes crank length into account, so it’s the only one of the three that compares bikes with different crank lengths fairly. It is the distance the bike travels for each unit of distance your foot travels.
Worked example: a 50/34 road bike with an 11-34 cassette
- Wheel: 700×28 → diameter 622 + 2×28 = 678 mm (26.69 in), circumference 2,130 mm.
- Top gear 50×11: ratio 4.545 → 121.3 gear inches, 9.68 m development, 52.3 km/h at 90 rpm.
- Bottom gear 34×34: ratio 1.00 → 26.7 gear inches, 2.13 m development, 11.5 km/h at 90 rpm.
- Gear range: 4.545 ÷ 1.00 = 455%. That is wide enough for steep climbs and still fast descents.
These are the calculator’s default inputs, so every number above appears in the gear chart.
Wheel and tire circumference chart
Gear inches and speed depend on the real outside diameter of the wheel, which is the rim’s ISO bead seat diameter plus twice the tire height (roughly equal to its width). Computed with the calculator’s own formula:
| Wheel and tire | ISO rim (mm) | Outside diameter | Circumference |
|---|---|---|---|
| 700×25c | 622 | 672 mm (26.5 in) | 2,111 mm |
| 700×28c | 622 | 678 mm (26.7 in) | 2,130 mm |
| 700×32c | 622 | 686 mm (27.0 in) | 2,155 mm |
| 700×40c gravel | 622 | 702 mm (27.6 in) | 2,205 mm |
| 700×45c gravel | 622 | 712 mm (28.0 in) | 2,237 mm |
| 29×2.2″ | 622 | 734 mm (28.9 in) | 2,306 mm |
| 29×2.4″ | 622 | 744 mm (29.3 in) | 2,337 mm |
| 650b×47 | 584 | 678 mm (26.7 in) | 2,130 mm |
| 27.5×2.4″ | 584 | 706 mm (27.8 in) | 2,218 mm |
| 26×2.1″ | 559 | 665 mm (26.2 in) | 2,089 mm |
| 20×1.75″ (BMX/folding) | 406 | 494 mm (19.4 in) | 1,552 mm |
| 16×1.35″ Brompton | 349 | 419 mm (16.5 in) | 1,316 mm |
Real tires vary by a few millimetres between models and pressures. If you want speedometer-level accuracy, roll the bike one full turn with you on it, measure the distance, and enter it as your rollout.
Road chainrings compared: 53/39 vs 52/36 vs 50/34 vs 48/35 vs 46/33
Each crankset is paired with the cassette it usually ships with, on a 700×28 wheel. “Climb speed” is the speed in the lowest gear at 70 rpm; “top speed” is in the highest gear at 100 rpm.
| Crankset + cassette | Lowest gear | Highest gear | Range | Climb speed @70 rpm | Top speed @100 rpm |
|---|---|---|---|---|---|
| 53/39 + 11-30 | 34.7″ | 128.6″ | 371% | 11.6 km/h | 61.6 km/h |
| 52/36 + 11-30 | 32.0″ | 126.2″ | 394% | 10.7 km/h | 60.4 km/h |
| 50/34 + 11-34 | 26.7″ | 121.3″ | 455% | 8.9 km/h | 58.1 km/h |
| 48/35 + 10-33 (SRAM) | 28.3″ | 128.1″ | 453% | 9.5 km/h | 61.3 km/h |
| 46/33 + 10-36 (SRAM) | 24.5″ | 122.8″ | 502% | 8.2 km/h | 58.8 km/h |
Modern 12-speed groupsets have converged: SRAM’s 10-tooth cog lets a smaller 48/35 or 46/33 crankset match the top end of an older 52/36 while giving easier climbing gears.
Which cassette? 11-28 vs 11-30 vs 11-34 vs 10-33 vs 10-36
Each cassette below is paired with a 50/34 crankset on 700×28 wheels. The “average step” is the typical jump in effort per shift on the cassette; under about 10% feels smooth on the road.
| Cassette (with 50/34) | Lowest gear | Highest gear | Range | Average step | Biggest jump |
|---|---|---|---|---|---|
| Shimano 11s 11-28 | 32.4″ | 121.3″ | 374% | 9.8% | 13.3% |
| Shimano 12s 11-30 | 30.3″ | 121.3″ | 401% | 9.6% | 14.3% |
| Shimano 12s 11-34 | 26.7″ | 121.3″ | 455% | 10.8% | 14.3% |
| SRAM AXS 10-33 | 27.5″ | 133.5″ | 485% | 11.5% | 17.9% |
| SRAM AXS 10-36 | 25.2″ | 133.5″ | 529% | 12.4% | 16.7% |
1× gearing for MTB and gravel
One-by drivetrains trade small steps for simplicity and a huge cassette. These are the most common combinations:
| Setup | Lowest gear | Highest gear | Range | Climb speed @70 rpm |
|---|---|---|---|---|
| MTB 30T + Eagle 10-52 (29×2.4) | 16.9″ | 87.9″ | 520% | 5.7 km/h |
| MTB 32T + Eagle 10-52 (29×2.4) | 18.0″ | 93.7″ | 520% | 6.0 km/h |
| MTB 32T + XT 10-51 (29×2.4) | 18.4″ | 93.7″ | 510% | 6.2 km/h |
| Gravel 40T + XPLR 10-44 (700×45) | 25.5″ | 112.1″ | 440% | 8.5 km/h |
| Gravel 42T + XPLR 10-44 (700×45) | 26.8″ | 117.7″ | 440% | 9.0 km/h |
Below about 22 gear inches, most riders can stay seated and keep traction on steep, loose climbs. That’s why 30–32 tooth chainrings with a 51 or 52 tooth cog dominate trail bikes.
Will your lowest gear get you up the hill?
Gearing is about cadence on climbs. The table uses an 83 kg rider and bike at 200 watts (a sustainable effort for a fit amateur) with road rolling resistance. It shows the speed and the cadence you’d be turning in common lowest gears:
| Gradient | Speed at 200 W | Cadence 34×28 | Cadence 34×34 | Cadence 33×36 |
|---|---|---|---|---|
| 6% | 12.6 km/h (7.8 mph) | 81 rpm | 98 rpm | 107 rpm |
| 8% | 9.9 km/h (6.2 mph) | 64 rpm | 78 rpm | 85 rpm |
| 10% | 8.1 km/h (5.1 mph) | 52 rpm | 64 rpm | 69 rpm |
| 12% | 6.9 km/h (4.3 mph) | 44 rpm | 54 rpm | 59 rpm |
| 15% | 5.6 km/h (3.5 mph) | 36 rpm | 44 rpm | 48 rpm |
Below 60 rpm most riders feel they’re grinding and lose efficiency; 70–90 rpm is comfortable for long climbs. If your number is in the 50s, go one or two cogs bigger or a smaller chainring. Use the climb check above with your own weight and power.
Speed at cadence chart
| Cadence | 50×11 | 50×17 | 34×21 | 34×34 |
|---|---|---|---|---|
| 60 rpm | 34.9 km/h (21.7) | 22.6 km/h (14.0) | 12.4 km/h (7.7) | 7.7 km/h (4.8) |
| 70 rpm | 40.7 km/h (25.3) | 26.3 km/h (16.3) | 14.5 km/h (9.0) | 8.9 km/h (5.6) |
| 80 rpm | 46.5 km/h (28.9) | 30.1 km/h (18.7) | 16.6 km/h (10.3) | 10.2 km/h (6.4) |
| 90 rpm | 52.3 km/h (32.5) | 33.8 km/h (21.0) | 18.6 km/h (11.6) | 11.5 km/h (7.1) |
| 100 rpm | 58.1 km/h (36.1) | 37.6 km/h (23.4) | 20.7 km/h (12.9) | 12.8 km/h (7.9) |
| 110 rpm | 63.9 km/h (39.7) | 41.3 km/h (25.7) | 22.8 km/h (14.1) | 14.1 km/h (8.7) |
| 120 rpm | 69.7 km/h (43.3) | 45.1 km/h (28.0) | 24.8 km/h (15.4) | 15.3 km/h (9.5) |
Cross-chaining, duplicates and gear steps
- Cross-chaining means using the big chainring with the biggest cogs, or the small ring with the smallest cogs, on a 2× drivetrain. The chain runs at a steep angle, which adds friction, noise and wear. The gear chart strikes these through.
- Near-duplicates. A 2×12 setup has 24 combinations, but typically only 16–18 genuinely different gears (18 for a 50/34 with an 11-34). Any two within 3% of each other are underlined, because they feel the same on the road.
- Steps. The percentage change between neighbouring cogs is what you feel when you shift. Tight steps (6–9%) let you hold your ideal cadence; jumps above 15% are noticeable, and are normal at the big end of a 1× cassette.
Fixie and single-speed riders: choose “Fixie” for skid-patch counts. The number of distinct places your rear tire skids is the cog size divided by the greatest common divisor of the chainring and cog. Ambidextrous skidders double it when the reduced chainring number is odd. 48×17 gives 17 patches; 46×16 gives 8, or 16 for ambidextrous skidding.
Common gearing mistakes
- Comparing gear ratios across wheel sizes. A 2.0 ratio on a 20-inch folding bike is far easier than 2.0 on a 29er. Compare gear inches or development instead.
- Ignoring tire size. Going from 25 mm to 45 mm tires raises every gear by about 6% on a 700c wheel.
- Judging a cassette by its biggest cog alone. The steps in the middle, where you spend most of your time, matter just as much.
- Forgetting the derailleur’s limits. Check the maximum cog and total capacity of your rear derailleur before fitting a bigger cassette.
- Counting 24 gears on a 2×12. Allowing for cross-chaining and near-duplicates, the real number is much lower.
Bike gear calculator FAQs
How do you calculate a bike’s gear ratio?
Divide the number of teeth on the chainring by the number of teeth on the rear cog. A 50-tooth chainring with an 11-tooth cog gives 50 ÷ 11 = 4.55, meaning the rear wheel turns 4.55 times per pedal revolution.
What are gear inches?
Gear inches = gear ratio × wheel diameter in inches. It describes a gear as the size of an equivalent direct-drive wheel, so it lets you compare bikes with different wheel sizes. On a 700×28 wheel, 50×11 is 121.3 gear inches and 34×34 is 26.7.
What is development or rollout?
Development is the distance the bike travels for one full pedal revolution: gear ratio × wheel circumference. 50×11 on a 700×28 wheel develops 9.68 metres per pedal turn.
How do I calculate speed from gear and cadence?
Speed (km/h) = development in metres × cadence × 60 ÷ 1000. At 90 rpm in 50×11 on a 700×28 wheel: 9.68 × 90 × 60 ÷ 1000 = 52.3 km/h (32.5 mph).
Is 50/34 or 52/36 better?
A 50/34 compact gives an easier lowest gear (about 6% lower than 52/36 with the same cassette), which suits hilly riding and most amateurs. A 52/36 mid-compact gives a slightly higher top gear and smaller front-shift jump, which suits stronger riders on flatter terrain.
Should I choose an 11-30 or 11-34 cassette?
An 11-34 gives a 13% easier lowest gear than 11-30, at the cost of slightly bigger jumps between the larger cogs. If you regularly ride climbs over 8–10% or carry luggage, choose 11-34; for flatter routes, 11-30’s tighter steps feel smoother.
What gear ratio is best for climbing?
For long climbs, most riders want a lowest gear of around 1:1 (for example 34×34) or lower, roughly 25–28 gear inches on a road bike, so they can keep 70–90 rpm. Mountain bikes go lower, under 20 gear inches, with 30–32 tooth chainrings and 51–52 tooth cogs.
What is cross-chaining?
Cross-chaining is running the big chainring with the biggest rear cogs, or the small chainring with the smallest cogs, on a 2× drivetrain. The chain runs at a steep angle, increasing friction, noise and wear. The gear chart strikes these combinations through.
How many gears does a 2×12 bike really have?
It has 24 combinations, but once cross-chained gears and near-duplicates (within 3% of each other) are removed, a typical 2×12 road setup has about 16–18 genuinely different gears; a 50/34 with an 11-34 has 18. The calculator counts them for your exact setup.
What is a good gear ratio for a fixie or single-speed?
Most urban fixed-gear and single-speed riders use a ratio around 2.6–2.9 (about 70–75 gear inches on a 700c wheel), for example 46×17 or 48×17. Choose a combination with many skid patches if you skid-stop, so tire wear is spread out.
Does tire size affect gearing?
Yes. A larger outside diameter raises every gear. Going from 700×25 to 700×45 increases the wheel diameter by about 6%, so each gear becomes about 6% harder and faster at the same cadence.
How do I measure my wheel’s rollout?
With the tire at riding pressure and you sitting on the bike, mark the tire and the ground, roll forward one full wheel revolution and measure the distance. Enter it in millimetres as the measured rollout for the most accurate speed figures.
Manzoor Ahmad
Founder, DexoCalc · 13+ years of web development and SEO experience
Manzoor builds and maintains every DexoCalc calculator. For this tool he took cassette tooth counts from Shimano and SRAM specifications, coded Sheldon Brown’s gear and skid-patch formulas and a standard cycling power model for the climb check, and generated each table on this page from the same engine that runs the calculator.
Sources & references
- Sheldon Brown. Gear theory, gear inches, gain ratios and skid patches. sheldonbrown.com
- SRAM Support. What is the tooth count of the XPLR 12-speed 10-44T cassettes? support.sram.com
- SRAM Red AXS E1 XG-1290 cassette cog sizes (10-28, 10-30, 10-33, 10-36). pushys.com.au
- SRAM GX Eagle XG-1275 10-52 cog sequence. rosebikes.com
- Shimano Ultegra CS-R8100 11-34 and Deore XT CS-M8100 10-51 sprocket combinations. velomine.com · meinhartje.com
- BikeCalc. Gear calculator and ISO 5775 tire sizing articles. bikecalc.com
Note: Wheel circumference is estimated from ISO rim size plus twice the tire width; real tires differ by a few millimetres. The climb check uses a standard physics model (gravity, rolling resistance, air drag and 97.6% drivetrain efficiency) with typical values for each bike type. Treat it as a guide; wind, surface and position change the result.