Bike Gear Ratio Calculator

How to use the bike gear ratio calculator

Four inputs drive every number on this page. Work top to bottom:

1. Front chainring teeth. The teeth on the ring you are pedalling. A compact road chainset is 50/34T, a gravel 1x is typically 38–42T, and a modern trail bike runs 30–34T.
2. Rear cassette cog. The sprocket you are in. Enter a single cog to check one gear, or the full range (11-34T, 10-52T) to see the whole spread.
3. Tyre size. This sets rolling circumference. A 700×25c road tyre, a 700×45c gravel tyre and a 29×2.4″ mountain bike tyre give noticeably different results from identical gearing.
4. Cadence (RPM). Your pedalling speed. Leave it at 90 RPM for road, and drop to 70–80 RPM for loaded climbing.

The calculator returns four outputs:

• Gear ratio. Wheel turns per pedal revolution.
• Gear inches. The universal comparison figure, normalised for wheel size.
• Development / rollout. Metres travelled per pedal stroke.
• Speed at cadence. Your km/h or mph at the RPM you set.

Understanding bike ratios: gear inches, development & rollout

Gear ratio = chainring teeth ÷ cassette teeth. A 50T ring on an 11T cog is 4.55, so the wheel spins four and a half times per pedal stroke. A 34T ring on a 34T cog is 1.00, a true one-to-one bailout. Ratio alone is fine for comparing cogs on your own bike, but it ignores wheel size entirely.

Gear inches = gear ratio × wheel diameter in inches, tyre included. This is the gold standard, because it folds wheel and tyre into one number you can compare across any two bikes. That same 50×11T on a 700×25c tyre (≈26.3″ diameter) is 120 gear inches. Put an identical drivetrain on 29×2.4″ rubber and it climbs to 133 gear inches, fully 11% taller from tyres alone. Rough anchors:

• Under 25 gear inches: steep climbing and loaded touring territory
• 50–75 gear inches: cruising and rolling terrain
• Over 110 gear inches: descending and sprinting

Development (rollout) = gear inches × 0.0798 metres. It is the distance you cover per pedal revolution: 9.5 m in that 50×11T road gear, 1.4 m in a 32×52T mountain bike crawler. Development is the most intuitive of the three because it maps straight onto speed: multiply by cadence and you have your km/h.

Popular drivetrain setup comparisons

Typical low and high gears for each riding style, on the tyre size that setup normally runs. Browse real cassettes and chainsets to check what your groupset actually offers.

• Road 2x stays the choice for tight steps between gears. Overlapping ratios across the two rings mean small cadence adjustments, which is why it survives in racing.
• Gravel 1x trades those tight steps for a clean chainline, no front derailleur and a huge spread. The 10-52T option buys climbing gears at the cost of big jumps in the middle.
• Mountain bike 1x prioritises the low end. An 18 gear inch crawler is unrideable on tarmac and essential on a loose 20% pitch.
• Single speed / fixed. Pick one number and live with it. Around 70 gear inches is the classic all-round urban choice: 63–66 for hills, 75+ for flat commutes.

Why gear ratios matter for cadence and climbing

Gearing is a lever. A lower ratio multiplies your force at the wheel. You turn the pedals more times for the same distance, but each stroke costs less. That trade lets you hold a steady cadence as the gradient changes instead of grinding.

Most riders are most efficient between 80 and 100 RPM. Below roughly 60 RPM, pedal force spikes and burns glycogen fast; above 110 RPM you leak energy to inefficiency. The practical rule: choose gearing that keeps you inside that window on your steepest regular climb, not on the flat.

To size a climbing gear, work backwards. On a 10% gradient most riders sustain 7–9 km/h. At 75 RPM that needs roughly 1.7 m of development, about 21 gear inches. A 34×34T road setup gives 26 gear inches, so it is under-geared for sustained steep climbs; a 34×36T, or a 1x 40×44T, gets much closer. The cycling power calculator shows how much power that climb actually costs at your weight.

Before you buy a smaller chainring, check your bottom bracket standard. A chainset swap is only a gearing decision once the frame interface matches.

Frequently asked questions

What is a good gear ratio for climbing hills?

Aim for a 1:1 ratio or lower, which is about 25 gear inches or less on 700c wheels. A 34T chainring with a 34T cog is the road baseline. For sustained gradients above 10%, or a loaded bike, go lower: a 40T ring with a 44T cog, or a 32T ring with a 50T cog on a mountain bike.

What is the difference between gear ratio and gear inches?

Gear ratio is chainring teeth divided by cog teeth and ignores your wheels. Gear inches multiplies that ratio by wheel diameter including the tyre, so it describes how hard the gear actually feels. Use gear ratio to compare cogs on one bike, and gear inches to compare two different bikes.

How do wheel and tyre sizes affect my effective gear ratio?

Your gear ratio does not change, but your effective gearing does. A larger tyre rolls further per wheel revolution, making every gear taller. Swapping 700×28c for 700×45c raises effective gearing by roughly 3%, which is noticeable on a climb. Recalculate gear inches whenever you change tyre width or wheel size.

Is 1x or 2x better for gear range?

A modern 1x drivetrain with a 10-52T cassette reaches about 520% range, beating a typical road 2x at around 455%. The 2x wins on step size: its overlapping ratios give small, smooth cadence changes, while 1x spreads the same range over fewer cogs and jumps harder between them. Choose 1x for simplicity and range, 2x for cadence precision.

Why does my top gear feel too tall to use?

If you cannot hold 85 RPM or more in your biggest gear on the flat, that gear is dead weight. Dropping from a 52T to a 50T chainring, or from an 11T to a 12T smallest cog, shifts the whole range toward gears you will actually use.