In the numerical evaluation system described in this paper, the nominal diameter of a sphere formed by a standardized solder specimen provides the zero per cent mark; the infinite thinness of the same solder mass spread as a film provides the 100 per cent mark, on a percentage scale. Intermediate values are determined by measurement of the height or thickness of the solder spots, obtained after melting, by means of a hand micrometer. The empirical spread-factor values thus obtained provide a simple, reproducible, visually significant numerical system. A general relationship to cos ϑ, where ϑ is the contact angle between liquid solder and solid base, is shown. Applications of this system for the evaluation of solders, fluxes, and metallic surfaces with respect to solderability are given.