It varies widely with the chamber pressure and other details of the engine design. Some examples of first-stage engines with their approximate nozzle ratios:
RD-180 (Atlas V) 36:1
F-1 (Saturn V) 16:1
Merlin 1D (Falcon 9) 16:1
SSME (STS, SLS) 77:1
For ideal performance, the expansion should reduce the exhaust pressure to be equal to the ambient atmospheric ...