经验关系是指依照观察得到，没有理论根据的关系及相关。经验关系只需和实际数据符合，不需要理论的基础。有时会找到经验关系式的理论解释，此时此关系式已不再只是经验关系式。因此相关不蕴涵因果，不过有时可以找到其因果性。有时经验关系式只是实际解的近似，多半会等于真实解泰勒展开式的前几项（实务上近似也可能已有相当的精确度）。有时会在以后发现经验关系只是在特定条件下的结果，此时较广泛的实际解简化为较简单的型式。

在历史上，经验关系式的发现相当重要，是发现其理论关系的第一步，偶尔会将此经验系数变成无因次量。

经验方程只是一个或多个经验关系式用方程表示的数学式。

In science, an empirical relationship is a relationship or correlation based solely on observation rather than theory. An empirical relationship requires only confirmatory data irrespective of theoretical basis. Sometimes theoretical explanations for what were initially empirical relationships are found, in which case the relationships are no longer considered empirical. Thus correlation is not causation but in some cases can be found to result from it. Other times the empirical relationships are merely approximations, often equivalent to the first few terms of the Taylor series of the "real" answer (though in practice these approximations may be so accurate it is difficult to tell they're approximations). Still other times the relationships may later be found to only hold under certain specific conditions, reducing them to special cases of more general relationship.