An experimental investigation has been conducted to develop the scaling law for the converging length of compressible round twin-jets. A twin-jet system with nozzle exit diameter D and normalized inter-nozzle spacing S/D of 3, 4, and 5 was investigated at ideally expanded jet Mach numbers Mj of 0.3, 0.5, 0.7, 1.0, 1.35, and 1.56. Scaling analysis performed for the converging length xcp revealed that the relationship xcp/D=g1(Mj,S/D) could be reduced to xcp/(S1.8/D0.8)=g2(Mj), where g1 and g2 are different functions. This scaling law extended to include both perfectly and imperfectly expanded sonic and supersonic twin-jets, leading to the relation xcp/(S1.8/D0.8), is proportional to (γMj2pepa)1/(jc+1), where pe/pa, γ, and jc are the nozzle expansion ratio, gas specific heat ratio, and index number, respectively. It has been documented that S1.8/D0.8 is the length scale to normalize xcp, which is valid for subsonic, sonic, and supersonic twin-jets. As such, for a given pe/pa and Mj, the dependence of xcp/D on S/D can be predicted using the scaling law xcp/(S1.8/D0.8). Further, the scaling law is discussed, leading to an interpretation of the physical meaning of the dimensionless parameter (γMj2pepa)1/(jc+1).