Ratios, gear inches, rollout and speed for any chainring and cassette. Set up two drivetrains — what you ride now and what you're thinking of — and see exactly where they differ.
Gear ratio is simply chainring teeth ÷ sprocket teeth — how many wheel turns you get per pedal turn. A 50-tooth ring on a 16-tooth sprocket is 50 ÷ 16 = 3.13.
Gear inches multiplies the ratio by the wheel diameter in inches — the old penny-farthing measure. Development (or rollout) is the ratio times the wheel circumference: the distance covered by one pedal stroke.
Speed is development × cadence: how far you roll each crank turn, times how many turns a minute. It assumes no freewheeling.
Wheel circumference comes from the standard roll-out figures for each tyre size, or your own measured roll-out if you pick Custom. Everything traces to plain geometry — there are no fudge factors.