How do you calculate a bike gear ratio?
Divide the chainring teeth by the sprocket teeth. A 50-tooth ring driving a 14-tooth cog is 50 ÷ 14 = 3.57 — the rear wheel turns 3.57 times per pedal revolution. That one number, times your wheel's circumference, times your cadence, is your speed; everything the chart above shows is that multiplication run across every gear you own.
A ratio ignores wheel size, so a 4.5 on a 26″ wheel is a shorter gear than a 4.5 on a 700c. Gear inches (ratio × wheel diameter) and meters of development (distance per crank revolution) both fold the wheel in, which is why fixed-gear riders and touring cyclists still swear by them. The chart above shows all of them — they order your gears identically; they just use different units. One gear only? The gear inches calculator adds skid patches, gain ratio and a hill check.
How fast is each gear? Speed at 90 rpm
| Sprocket | 50t ring | 34t ring |
|---|---|---|
| 30t | 11.9 mph | 8.1 mph |
| 27t | 13.2 mph | 9.0 mph |
| 24t | 14.9 mph | 10.1 mph |
| 21t | 17.0 mph | 11.6 mph |
| 19t | 18.8 mph | 12.8 mph |
| 17t | 21.0 mph | 14.3 mph |
| 15t | 23.8 mph | 16.2 mph |
| 14t | 25.5 mph | 17.4 mph |
| 13t | 27.5 mph | 18.7 mph |
| 12t | 29.8 mph | 20.2 mph |
| 11t | 32.5 mph | 22.1 mph |
Compact 50/34 crank, Shimano 11-30 cassette, 700×28 wheel, 90 rpm — computed by the calculator above, which handles any drivetrain, wheel and cadence (and km/h).
Read the top row carefully: 50×11 at 90 rpm is 32.5 mph. Unless you sprint or race downhill, that's a gear you coast in — which is why modern gearing keeps sliding lower, and why the bottom of the cassette matters more than the top for almost everyone.
What cadence do I need to hold 20 mph?
The same math runs backward: cadence = speed ÷ (ratio × circumference). Here's 20 mph in every 50-ring gear of that compact setup — the difference between spinning and grinding is just where you are on the cassette:
| Gear | Cadence for 20 mph |
|---|---|
| 50 × 30t | 151 rpm |
| 50 × 27t | 136 rpm |
| 50 × 24t | 121 rpm |
| 50 × 21t | 106 rpm |
| 50 × 19t | 96 rpm |
| 50 × 17t | 86 rpm |
| 50 × 15t | 76 rpm |
| 50 × 14t | 71 rpm |
| 50 × 13t | 65 rpm |
| 50 × 12t | 60 rpm |
| 50 × 11t | 55 rpm |
700×28 wheel. Most riders self-select 80–95 rpm on the flat; pick the gear that puts your target speed in that band and shift as the road tilts. The calculator's cadence view runs this for every gear at any speed.
What is a good gear range?
Range is your highest ratio divided by your lowest — the compact × 11-30 above spans 401%, meaning the hardest gear is about four times the easiest. A 1x gravel setup (40t × 10-44) reaches 440% with no front shifts, and an Eagle mountain drivetrain (32t × 10-52) stretches to 520%. More range costs bigger jumps between gears — that trade, and whether 1x or 2x suits you, is exactly what the 1x vs 2x calculator puts side by side.
On the compact × 11-30 above, 5 of the 22 chainring-sprocket pairings land within 4% of a gear on the other ring — closer than one cassette step, so they're duplicates in practice. That's normal for every 2x drivetrain, and it's why "22-speed" was always marketing: you're buying 17 distinct gears and the convenience of reaching them from either ring.
Does wheel size change my gearing?
Yes — the same drivetrain on a smaller wheel is geared lower, which is exactly what gear inches were invented to expose. The same 40t × 10-44 setup on three wheels:
| Wheel | Circumference | Low gear (40×44) | Top speed at 90 rpm |
|---|---|---|---|
| 700c / 29″ × 40 mm | 2205 mm | 25.1 in | 29.6 mph |
| 650b / 27.5″ × 47 mm | 2130 mm | 24.3 in | 28.6 mph |
| 26″ × 55 mm | 2102 mm | 23.9 in | 28.2 mph |
Gear inches = ratio × overall wheel diameter; typical tire widths per wheel size. Swapping 700c for 650b wheels lowers your whole range a step — for free.
What's a good lowest gear for climbing?
The rule of thumb that survives contact with real hills: an unloaded road bike wants a low gear near 1:1 (34×34, say), and loaded touring or steep gravel wants well under it. At 1:1 on a 700×28 wheel, 60 rpm moves you 4.8 mph — about walking pace with margin to sit and spin. If your current lowest gear forces you under ~60 rpm on the climbs you actually ride, the fix is a bigger cassette or smaller ring, not more heroics. Run your own numbers in the chart above; the low-gear cell is the one that decides whether a climbing day is hard or miserable.
How the numbers are calculated
Ratios, gear inches and development follow the standard conventions Sheldon Brown documented; speed is development × cadence. Wheel circumference is geometric — (rim diameter + twice the tire width) × π — which lands within about 1% of published rollout charts (700×25 computes to 2,111 mm, the number on every bike computer chart). Real rollout shifts slightly with pressure and load, so if you're calibrating a computer rather than choosing a cassette, measure a loaded wheel revolution instead. Cassette presets use the manufacturers' published sprocket sequences; if yours differs, type the sprockets in directly.