For multipass arc welding we formulated and obtained in analytical form general equations of dependency between welding process's thermal efficiency as well as cross-sectional area of a weld and technological welding parameters. These equations also represent, besides the known parameters, a mutual influence of electrode position relative to melted bath and size of melted metal's interlayer under electrode, as well as electrode stick-out and the chemical composition of shielding gas. Obtained analytical dependences might be used as a part of a software while working on adaptive welding systems.