Meters of development times cadence times 60 is meters per hour. Divide by 1,609.344 for miles per hour. At 90 rpm, a 50/11 on a 700c x 25 is a little over 30 mph. The same cadence in a 34/28 is a walking climb.
The free line is that one gear at the cadence you type. $5 adds 60, 70, 80, 90, 100, and 110 rpm for every cog, which is the table you tape to a stem.
On a climb, the check works the other way. Watts, weight, and grade produce a speed, and the chart finds the cog that keeps cadence between 60 and 100.
Gear is a rollout chart from the wheel and the teeth you enter. Tire pressure, wind, and a worn cassette change the real speed. It is not a fit session and it does not size a frame.