Bike Gear Calculator — Ratio, Speed at Cadence & Gear Inches
Work out gear ratio, speed at any cadence and gear inches from chainring, cog and wheel size — or paste a whole cassette for a full gear table.
🔒 Runs entirely in your browser. Your input and output are never sent to a server or stored — fully private.
Speed = wheel circumference × gear ratio × cadence. Circumference values are typical for each tire size — actual rollout varies with tire pressure and load.
About this tool
This bicycle gear calculator turns a chainring and cog combination into a gear ratio, gear inches and, with a wheel size and cadence, your speed. Enter front teeth, rear teeth, pick your wheel (700×25c, 26-inch, 650b and more) and a pedalling cadence, and it shows how fast that gear rolls and how it compares. A cassette mode takes a list of cog sizes and builds a table so you can see the whole range and the jumps between gears. Great for choosing gearing, spotting duplicate ratios, or planning a climb. Runs entirely in your browser.
Frequently asked questions
What is the difference between gear ratio and gear inches?
Gear ratio is simply front teeth ÷ rear teeth (50/25 = 2.0) — one pedal turn spins the wheel twice. Gear inches multiply that ratio by the wheel's diameter in inches, a historic measure from penny-farthing days that lets you compare gearing across different wheel sizes: a high number means a harder, faster gear. Speed then also needs your cadence. All three describe the same thing from different angles; use whichever your riding community prefers.
How do I use the speed and cassette features?
Speed needs a cadence (pedal RPM): speed = wheel circumference × ratio × cadence. At 90 rpm on 50/25 with a 700×25c wheel you roll about 22.8 km/h. Real cruising cadence is usually 80–100 rpm. The cassette mode takes a comma-separated list of your rear cogs (e.g. 11,13,15,17,19,21) and prints ratio and speed for each at your cadence, so you can see your top-end gear, your climbing gear and whether any jumps between sprockets feel too big.
Is the calculation done locally?
Yes — it is all JavaScript in your browser, so nothing you enter is uploaded or stored, and it works offline once the page has loaded. Note that predicted speed is on flat ground with no wind and assumes you can hold the cadence; real speed depends on gradient, wind, rolling resistance and your legs.