The compression ratio is the output pressure divided by the input pressure (in absolute pressures).
single stage oil injected screw compressors typically have an output pressure of 8 to 14 bar absolute (7 – 13 bar relative).
In which case the compression ratio is also in the range of 7 to 14.
Although higher pressure ratio’s can be achieved with oil-injected screw compressors (often in portable diesel compressors).
Hope this answers your questions 🙂