Divide the chainring by the cog, then multiply by the wheel. That is gear inches if the wheel is in inches, and development if the wheel is the tire circumference in meters. Speed is the development times cadence, turned into miles per hour.
A 50/34 with an 11-28 is not the same bike as a 52/36 with an 11-34. The second has a taller top end and an easier low gear. This calculator charts both and says which one climbs lower.
The tallest gear at one cadence is free. $5 unlocks every cog, the comparison, a climbing check, and a CSV. Long-ride training lives in Century Plan.
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.