Why the list has gaps
There is no standard 55 A or 65 A breaker. The list is a fixed set of manufactured ratings, and the gaps widen as the numbers grow — 15, 20, 25, 30, 35, 40, 45, 50, then a jump to 60. Where a calculated load falls between two, the general rule is to round up to the next standard rating, subject to conditions and exceptions that depend on the circuit type.
Sizing direction
A common misunderstanding is that the breaker protects the equipment. It protects the conductor. The breaker rating must not exceed what the conductor can safely carry — which is why the conductor is sized first and the overcurrent device follows, not the other way round.
The full list continues to 6000 A: 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000 A.